What is prenatal care

Prenatal care is an important part of a healthy pregnancy. Individual prenatal care is intended to prevent poor perinatal outcomes and provide education to women throughout pregnancy, childbirth, and the postpartum period through a series of one-on-one encounters between a woman and her obstetrician or other obstetric care provider. The American College of Obstetricians and Gynecologists recommends routine regularly scheduled visits that consist of objective assessments, testing, maternal support, and education ¹.

Whether you choose a family physician, obstetrician, midwife or group prenatal care, here’s what to expect during the first few prenatal appointments. Regular prenatal examinations are a top priority during any pregnancy. They are important both for monitoring your own and your baby’s health and for giving you and your health professional time to build a working relationship.

Table 1. Components of Routine Prenatal Examinations

Component	Comments
Abdominal palpation	Abdominal palpation (Leopold maneuvers) can be used to assess fetal presentation beginning at 36 weeks’ gestation; it is less accurate earlier in pregnancy
Blood pressure measurement	Although most guidelines recommend blood pressure measurement at each prenatal visit, further research is required to determine the optimal frequency
Evaluation for edema	Edema is defined as greater than 1+ pitting edema after 12 hours of bed rest, or weight gain of 2.3 kg (5 lb) in one week
	Edema occurs in 80% of pregnant women and lacks specificity and sensitivity for diagnosing preeclampsia
Fetal heart rate	Auscultation for fetal heart rate is recommended at each prenatal visit to confirm a viable fetus, although there is no evidence of other clinical or predictive value
Fundal height measurement	Measurement of fundal height is recommended at each prenatal visit beginning at 20 weeks and should be plotted for monitoring purposes
	Measurement is subject to inter- and intraobserver error
Urinalysis	Some guidelines recommend routine dipstick urinalysis at each prenatal visit, whereas others no longer recommend it
	Testing does not reliably detect proteinuria in patients with early preeclampsia; trace glycosuria is unreliable for the detection of gestational diabetes
Weight measurement	Maternal height and weight should be measured at the first prenatal visit to determine body mass index, and weight should be measured at all subsequent visits
	Patients who are underweight or overweight have known risks, such as anemia and gestational diabetes, and counseling should be provided to guide optimal weight gain

[Source ² ]

Many women have prenatal visits every 4 to 6 weeks until week 28 of pregnancy. Then the visits become more frequent. This is often every 2 to 3 weeks through week 36 of pregnancy. In the final month of pregnancy, you likely will see your doctor every week. You may have a different schedule if you have a medical problem or are a teen.

At different times in your pregnancy, you will have examinations and tests. Some are routine. Others are done only when there is a chance of a problem. Everything healthy you do for your body helps your growing baby. Rest when you need it. Eat well, drink plenty of water, and exercise regularly.

Your first prenatal care visit is likely to be more extensive than later prenatal checks. Your health professional will take your medical history and do a complete physical examination.

Medical history

Your medical history helps your health professional plan the best possible care for your pregnancy and childbirth. It includes:

• Your menstrual history, including your age when menstruation started, whether your cycles are regular, and the date of your last menstrual period.
• Your reproductive history. This includes:
• Any previous pregnancies, abortions, miscarriages, or stillbirths.
• Problems with previous pregnancies.
• Any problems with reproductive organs.
• Family health conditions, such as heart disease or genetic defects.
• All vaccinations, surgeries, and serious illnesses you have had.

Physical examination

Your complete physical examination will include:

• Weight and blood pressure measurement.
• A pelvic examination.
• A Pap smear (if not done recently).

Urine tests

A urine test can check for:

• Sugar, a sign of gestational diabetes.
• Protein, a sign of pre-eclampsia.
• Bacteria, a sign of urinary tract infection (UTI), which can be present without symptoms. UTI is common during pregnancy and, if untreated, may lead to kidney infection.

Blood tests

Blood testing may include:

• Blood typing (A, B, or O, and Rh factor). If you are Rh-negative and the father is Rh-positive, your fetus may have Rh-positive blood, which can lead to problems with Rh sensitization. For more information, see the topic Rh Sensitization During Pregnancy.
• Complete blood count (CBC), which checks hemoglobin and hematocrit to make sure you don’t have iron deficiency anemia.
• Checking for immunity to German measles (rubella).

You may also be screened for:

• Hepatitis B. If you have a hepatitis B infection, your baby will receive the hepatitis vaccine and hepatitis B immune globulin (HBIG) within 12 hours of birth.
• Hepatitis C.
• Rubella
• Tuberculosis (TB)
• Diseases that are passed down through families (genetic disorders). Screening tests for genetic disorders include those for:
  • Cystic fibrosis.
  • Sickle cell disease.
  • Tay-Sachs disease.
• Sexually transmitted infections (STIs) . Sexually transmitted infections during pregnancy have been linked to miscarriage, premature birth, low birth weight, and stillbirth. Many health professionals routinely test for the sexually transmitted infections gonorrhea and chlamydia. If test results show that you have an sexually transmitted infection, your health professional will discuss treatment with you.
• The sexually transmitted infection syphilis.
• The human immunodeficiency virus (HIV). This is done only with your consent or request. Early detection and treatment lowers the chance that the baby will get HIV from the mother. The American College of Obstetricians and Gynecologists recommend that all pregnant women be screened for HIV infection to help prevent fetal infection ¹.
• Thyroid disease. Many women have thyroid tests done if they have a personal or family history of thyroid problems.
  Depression. Not treating depression can cause problems during pregnancy and birth. To find out if you are depressed, your health professional will ask you questions about your health and your feelings.

If your pregnancy is going well, you will have a regular schedule of prenatal checkups. These will become more frequent as you near your due date. A general example of such a schedule is as follows.

• After the first prenatal visit, every 4 weeks till week 28 of pregnancy
• Every 2 to 3 weeks through week 36 of pregnancy
• Every week during the final month of pregnancy

You may have more frequent prenatal examinations if you:

• Began your pregnancy with a pre-existing medical problem.
• Develop complications during your pregnancy.
• Are a teen.

Does planned parenthood provide prenatal care?

Yes. You can also get prenatal care at some Planned Parenthood health centers (https://www.plannedparenthood.org/health-center).

Why is prenatal care important?

Regular prenatal visits are very important during any pregnancy. These quick office visits may seem simple and routine. But they can help you and your baby stay healthy. Your doctor is watching for problems that can only be found by regularly checking you and your baby. The visits also give you and your doctor time to build a good relationship.

Prenatal care is important to reducing rates of premature birth

Despite progress on many fronts, including advances in science and technology and use of best practices, the US infant mortality rate stubbornly remains at nearly 7 deaths in the first year of life for every 1,000 live births ³.

Birth before 37 weeks, 0 days gestation is considered preterm. The U.S. experienced a 20% increase in premature births from 1990–2006 ⁴. In 2008, more than half a million babies were born prematurely in the United States – 1 in 8 births ⁵.

Preterm labor can occur in any pregnancy without warning. Women who have little or no prenatal care, obese women, and those who have had preterm labor before are at increased risk.

Preterm birth is the leading cause of newborn death and disability

About two-thirds of all infant deaths (0–1 years old) are among preterm infants ⁶.

Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It’s also a good idea to know your test results and keep a list of the medicines you take.

Babies who survive often have lifetime health complications, including breathing problems, cerebral palsy and intellectual disabilities. Late-preterm infants (babies born between 34 and 37 weeks gestation) are 4 times more likely than term infants to have at least 1 medical condition and 3.5 times more likely to have 2 or more conditions ⁷. Approximately 8% of preterm babies have a major birth defect ⁸. Preterm birth is a leading cause of neurological disability, including cerebral palsy in children.

Infants born early have higher rates of hospitalization and illness than full-term babies. Growth and development in the last part of pregnancy are vital to the baby’s health. The earlier the baby is born, the greater the chance he or she will have health problems. Preterm babies tend to grow more slowly than term babies. They also may have problems with their eyes, ears, breathing, and nervous system. Learning and behavioral problems are more common in children who were born before 39 weeks ⁹.

Prevention

Prenatal care often consists of identifying fetal problems and arranging modified prenatal care to best manage the outcome via surveillance in an appropriate site, care by maternal-fetal medicine subspecialists with consultation by pediatric/fetal surgeons, and delivery in the best place and under the best circumstances so that newborn care specialists can give the baby the best chance of survival.

Prenatal care has the potential to identify and treat early indicators of premature birth, leading to healthier pregnancies, healthy moms and healthy babies.

When to start prenatal care?

Women are strongly advised to begin prenatal care as soon as they know they are pregnant. Prenatal care continues to be the primary way to identify problems during pregnancy, giving your healthcare providers a way to assess and manage risks for preterm labor and other threats to the health of the mother and her baby.

What happens during a prenatal care visit?

• You will have blood pressure checks, along with urine tests. You also may have blood tests. If you need to go to the bathroom while waiting for the doctor, tell the nurse. He or she will give you a sample cup so your urine can be tested.
• You will be weighed and have your belly measured.
• Your doctor may listen to your baby’s heartbeat with a special stethoscope.
• In your second trimester, your doctor will check your blood sugar (glucose tolerance test) for diabetes that can occur during pregnancy. This is gestational diabetes, which can harm your baby.
• You will have tests to check for infections that could harm your newborn. These include group B streptococcus and hepatitis B.
• Your doctor may do ultrasounds to check for problems. This also checks your baby’s position. An ultrasound uses sound waves to produce a picture of your baby.
• You may have other tests at any time during your pregnancy.
• Use your visits to discuss with your doctor any concerns you have.

Your first prenatal examination gives your doctor or midwife important information for planning your care. You’ll have a pelvic examination and urine and blood tests. You’ll also have your blood pressure and weight checked. The urine and blood tests are used for a pregnancy test and to tell whether you have low iron levels (are anemic) or have signs of infection.

At each prenatal visit you’ll be weighed, have your belly measured, and have your blood pressure and urine checked. Go to all your appointments. Although these quick office visits may seem simple and routine, your doctor is watching for signs of possible problems like high blood pressure.

In some medical centers, you can have screening in your first trimester to see if your baby has a chance of having Down syndrome or another genetic problem. The test usually includes a blood test and an ultrasound.

During your second trimester, you can have a blood test (triple or quadruple screen test) to see if you have a higher-than-normal chance of having a baby with birth defects. Based on the results of the tests, you may be referred to a geneticist for further discussion. Or you may have other tests to find out for sure if your baby has a birth defect.

Late in your second trimester, your blood sugar will be checked for diabetes during pregnancy (gestational diabetes). Near the end of your pregnancy, you will have tests to look for infections that could harm your newborn.

Prenatal care guidelines

Standard elements of prenatal care include a routine physical examination (including pelvic examination) at the initial visit, maternal weight and blood pressure at all visits, fetal heart rate auscultation after 10 to 12 weeks with a Doppler monitor or after 20 weeks with a fetoscope, fundal height after 20 weeks, and fetal lie by 36 weeks ¹⁰.

A pelvic examination at the initial visit is useful in detecting reproductive tract abnormalities and to screen for sexually transmitted infections. Routine pelvimetry is not useful. Papanicolaou (Pap) smears should be offered during prenatal care at recommended intervals based on age and Papanicolaou smear history, but do not need to be repeated during pregnancy ¹¹. Although promotion of breastfeeding is critical, there is no clear evidence to support clinical breast examinations. However, breast examinations may help to proactively address breastfeeding concerns or problems ¹². Although assessment of fundal height and fetal heart tones at every visit is recommended in multiple guidelines, the effect on outcomes is not clear ¹³.

Early body mass index measurement, using prepregnancy height and weight, is important to guide further nutritional counseling and to address the risks of obesity and diabetes ¹⁴. Measurement of blood pressure at each prenatal visit will identify chronic hypertension and hypertensive disorders that may develop during pregnancy, such as preeclampsia and gestational hypertension ¹³. These disorders are often asymptomatic.

Periodontal disease is associated with increased risk of preterm birth, and an oral examination is often included in the first prenatal visit. However, treatment does not change outcomes ¹⁵.

Pregnant women should be counseled about proper diet, as well as folic acid supplementation. Table 2 summarizes dietary guidelines for pregnant women. Table 3 includes other counseling topics during prenatal care.

Table 2. General Dietary Guidelines for Pregnant Women

Component	Guidelines	Comments
Artificial sweeteners	Minimize intake of food and drinks containing saccharin	Saccharin is known to cross the placenta and may remain in fetal tissue Aspartame, sucralose, and acesulfame-K are probably safe
Caffeine	Limit consumption to 150 to 300 mg per day; moderate amounts are probably safe	Observational studies show an association between high caffeine consumption and spontaneous abortion and low birth weight Studies may be limited by confounding exposures that were unobserved
Calorie intake	Most pregnant women require an additional 300 to 400 calories per day	Weight gain guidelines have varied and are based on limited data
Dairy	Avoid unpasteurized dairy products and soft cheeses (e.g., feta, Brie, Camembert, blue-veined cheeses, Mexican queso fresco)	Risk of Toxoplasma and Listeria contamination, based on case reports
Delicatessen foods	Avoid delicatessen foods, pâté, and meat spreads	Risk of Listeria contamination, based on case reports
Eggs	Avoid raw eggs (e.g., in Caesar salad, eggnog, and raw cookie dough)	Risk of salmonella contamination, based on case reports
Folic acid	Folic acid supplementation (400 mcg daily) should be initiated as soon as possible, preferably four weeks before conception Women taking folate antagonists or who have carried a fetus with a neural tube defect should take 4 mg of folic acid daily	Helps prevent neural tube defects
Fruits and vegetables	Fruits and vegetables should be washed before eating Cutting boards, dishes, utensils, and hands should be washed with hot, soapy water after contact with unwashed fruits and vegetables	Risk of Toxoplasma and Listeria contamination, based on case reports
Herbal teas	Avoid teas containing chamomile, licorice, peppermint, or raspberry leaf	Some herbal teas have been associated with adverse outcomes, such as uterine contraction, increased uterine blood flow, and spontaneous abortion, in low-quality studies Teas containing ginger, citrus peel, lemon balm, and rose hips are probably safe in moderation
Leftover foods	Thoroughly reheat before eating	Risk of Listeria contamination, based on case reports
Meat	Avoid undercooked meat; hot dogs and cold cuts should be heated until steaming hot Cutting boards, dishes, utensils, and hands should be washed with hot, soapy water after contact with uncooked meat Liver and liver products should be eaten in moderation	Risk of Toxoplasma and Listeria contamination with undercooked meats, based on case reports Excessive consumption of liver products could cause vitamin A toxicity
Seafood	Avoid shark, swordfish, mackerel, tilefish, and tuna steaks; limit intake of other fish (including canned tuna) to 12 oz per week Avoid refrigerated smoked seafood Avoid raw fish and shellfish Eat farmed salmon in moderation	Exposure to high levels of mercury in certain fish can lead to neurologic abnormalities in pregnant women and infants
		Risk of Listeria contamination with refrigerated smoked seafood, based on case reports
		Risk of exposure to parasites and Norovirus with raw fish and shellfish, based on case reports
		Increased levels of organic pollutants, including polychlorinated biphenyls and dioxins, have been found in farmed salmon

[Source ² ]

Table 3. Counseling Topics in Pregnancy

Topic		Comments
Air travel		Air travel generally is safe for pregnant women up to four weeks before the due date; however, long flights are associated with an increased risk of venous thrombosis
		Availability of medical resources at the destination should be considered
		The Centers for Disease Control and Prevention provides information for pregnant travelers at (https://wwwnc.cdc.gov/travel/yellowbook/2018/advising-travelers-with-specific-needs/pregnant-travelers)
Breastfeeding		Breastfeeding should be recommended as the best feeding method for most infants
		Breastfeeding contraindications include maternal human immunodeficiency virus infection, chemical dependency, and use of certain medications
		Structured behavior counseling, one-on-one needs-based counseling, and breastfeeding education programs increase breastfeeding success
Childbirth education		Childbirth education is a common part of prenatal care in the United States
		Although it may increase confidence, it does not change the experience of labor or birth outcomes
Exercise		At least 30 minutes of moderate exercise on most days of the week is a reasonable activity level for most pregnant women
		Pregnant women should avoid activities that put them at risk of falls or abdominal injuries
Fetal movement counts		Routine counting of fetal movements should not be performed
		This has been shown to increase the patient’s anxiety and results in more triage evaluations, prenatal testing, and interventions without improving outcomes
Hair treatments		Although hair dyes and treatments have not been explicitly linked to fetal malformation, they should be avoided during early pregnancy
Heavy metals		Exposure to heavy metals should be avoided during early pregnancy because of the potential for delayed fetal neurologic development
Herbal therapies		Pregnant women should avoid herbal therapies with known harmful effects to the fetus, such as ginkgo, ephedra, and ginseng, and should be cautious of substances with unknown effects
Hot tubs and saunas		Hot tubs and saunas should be avoided during the first trimester, because heat exposure during early pregnancy has been associated with neural tube defects and miscarriage
Labor and delivery		Pregnant women should be counseled about what to do when their membranes rupture, what to expect when labor begins, strategies to manage pain, and the value of having support during labor
Medications (prescription and over-the-counter)		Risks and benefits of individual medications should be reviewed
		Few medications have been proven safe for use during pregnancy, particularly during the first trimester
Radiation		Pregnant women should avoid ionizing radiation, because it may affect fetal thyroid development
		Adverse fetal effects are not associated with radiography that is in a normal diagnostic range (less than 50 mGy) and that avoids direct abdominal views; ultrasonography; or use of microwaves, computers, or cell phones
Seat-belt use		Pregnant women should use a three-point seat belt
		Less than one-half of pregnant women use a seat belt, and less than one-third receive physician counseling about seat-belt use
Sex		Most women may continue to have sex during pregnancy; however, in certain situations (e.g., placenta previa), avoiding sex is generally recommended
Solvents		Pregnant women should avoid exposure to solvents, particularly in areas without adequate ventilation
		Exposure to solvents has been associated with an increase in miscarriage rates
Substance use
	Alcohol	Pregnant women should be screened for alcohol use; no amount of alcohol consumption has been proven safe during pregnancy
		Counseling is effective in decreasing alcohol consumption in pregnant women and associated infant morbidity
	Illicit drugs	Pregnant women should be informed of the potential adverse effects of illicit drug use on the fetus
		Pregnant women who use illicit drugs often require specialized interventions
		Admission to a detoxification program may be indicated, as well as methadone therapy in women addicted to opiates
	Tobacco	Pregnant women should be screened for tobacco use, and individualized, pregnancy-tailored counseling should be offered to smokers
		Smoking cessation counseling and multicomponent strategies are effective in decreasing the incidence of low-birth-weight infants
Workplace issues		Although working in general is safe during pregnancy, some working conditions, such as prolonged standing and exposure to certain chemicals, are associated with pregnancy complications

[Source ² ]

Dating of Pregnancy and Routine Ultrasonography

Accurate dating as early as possible in the pregnancy is important for scheduling screening tests and planning for delivery ¹³. Estimated date of confinement is based on the first day of the last menstrual period plus 280 days. Urine pregnancy tests qualitatively test for beta subunit of human chorionic gonadotropin and are usually positive within one week of missed menses ¹⁶.

Early ultrasonography should be performed if the patient has irregular cycles or bleeding, if the patient is uncertain of the timing of her last menstrual period, or if there is a discrepancy in the size of her uterus compared with the gestational age. Ultrasonography can accurately date the pregnancy, evaluate for multiple gestation, and reduce the likelihood of unnecessary labor induction for postterm pregnancy ¹⁷. Ultrasound dating is considered accurate to within four to seven days in the first trimester, 10 to 14 days in the second trimester, and 21 days in the third trimester ¹⁸. Pregnancy dating should be confirmed with auscultation of fetal heart tones between 10 and 12 weeks, and with fetal quickening between 16 and 18 weeks in women who have been pregnant before or between 18 and 19 weeks in first pregnancies.

A randomized trial comparing routine screening ultrasonography (between 15 and 22 weeks and again at 31 to 35 weeks) performed only for medical indications showed no difference in perinatal outcomes (e.g., fetal or neonatal death, neonatal morbidity) ¹⁹. A recent Cochrane review, however, showed that ultrasonography before 24 weeks reduces missed multiple gestation and inductions for postterm pregnancies ¹⁸. There is no other scientific support for routine ultrasonography in uncomplicated pregnancies. It is the standard of care in most U.S. communities to offer a single ultrasound examination at 18 to 20 weeks’ gestation, even if dating confirmation is not needed. This is the optimal time for fetal anatomic screening,23 although the sensitivity of ultrasonography for structural anomalies is poor (overall sensitivity from 11 studies = 24.1%, range = 13.5% to 85.7%) ¹³.

Alloimmunization

The risk of developing alloimmunization for an RhD-negative woman carrying an RhD-positive fetus is approximately 1.5%. This risk can be reduced to 0.2% with Rho(D) immune globulin (RhoGam) ¹³. Testing for ABO blood group and RhD antibodies should be performed early in pregnancy. Rho(D) immune globulin, 300 mcg, is recommended for nonsensitized women at 28 weeks’ gestation, and again within 72 hours of delivery if the infant has RhD-positive blood ²⁰.

Rho(D) immune globulin should also be administered if the risk of fetal-to-maternal transfusion is increased (e.g., with chorionic villus sampling, amniocentesis, external cephalic version, abdominal trauma, or bleeding in the second or third trimester). Although alloimmunization is uncommon before 12 weeks’ gestation, women with a threatened early spontaneous abortion may be offered Rho(D) immune globulin, 50 mcg ²⁰.

Anemia

Iron deficiency anemia is associated with an increased risk of preterm labor, intrauterine growth retardation, and perinatal depression ²¹. All pregnant women should be screened for anemia early in pregnancy and treated with supplemental iron if indicated ¹³.

The U.S. Preventive Services Task Force has found insufficient evidence to recommend for or against routine iron supplementation ²². Multivitamins alone have demonstrated no benefit over iron and folate supplementation ²³. Pregnant women with anemia other than iron deficiency or who do not respond to iron supplementation within four to six weeks should be evaluated for other conditions, including malabsorption, ongoing blood loss, thalassemia, or other chronic diseases.

Genetic Testing and Neural Tube Defects

Down syndrome (trisomy 21 syndrome) occurs in one per 1,440 births in women 20 years of age and one per 32 births in women 45 years of age ²⁴. Most organizations recommend that all pregnant women be offered aneuploidy screening. Traditional serum screening for Down syndrome is complicated by high false-positive rates (90% to 95% of positive results are false). False-negative results are also possible. Patients should be given sufficient information to make an informed decision ²⁵.

Invasive genetic testing (amniocentesis or chorionic villous sampling) should be offered to women who are 35 years or older. At 35 years of age, the risk of Down syndrome (one per 338 births) is similar to that of fetal loss due to amniocentesis ²⁴. It is common to offer invasive testing to women 35 years and older without first performing screening tests; however, screening tests can be used for risk stratification to help a woman decide if she wants invasive testing ¹³. Options for aneuploidy screening include nuchal translucency testing with serum testing (nine to 11 weeks’ gestation) and later serum testing alone (15 to 19 weeks’ gestation). There are a variety of combinations of such tests, and results are generally reported as the risk of aneuploidy. All screening tests have a positive rate of approximately 5% (most of which are false positives) and a detection rate of 69% to 87% ¹³. Table 4 compares screening tests for Down syndrome ²⁴.

Table 4. Prenatal Screening Tests for Down Syndrome

Test	Markers	Term risk cutoff	Sensitivity (%)	Specificity (%)	Positive predictive value (%)
First trimester screening	Nuchal translucency, free β-hCG, PAPPA, maternal age	1 in 325	83	95	4
Quadruple screening (second trimester)	Unconjugated estriol, α-fetoprotein, free β-hCG, inhibin A, maternal age	1 in 385	77	95	2
Integrated screening (first and second trimesters)	Nuchal translucency, PAPPA, α-fetoprotein, unconjugated estriol, free β-hCG/total hCG, inhibin A, maternal age	1 in 200	87	98

Abbreviations: hCG = human chorionic gonadotropin; PAPPA = pregnancy-associated plasma protein A.

[Source ²⁶ ]

If a screening test is positive for Down syndrome, the woman should be offered amniocentesis (15 weeks’ gestation or later) or chorionic villous sampling (11 to 13 weeks). The rates of excess fetal loss with these two procedures are similar ¹⁶. In centers where both procedures are available, women can consider earlier genetic testing options ¹³.

A combination of serum and nuchal translucency testing can also screen for other trisomy syndromes, such as 13 and 18. Most laboratories can report the risk of trisomy 18 syndrome using serum testing. Protocols for the detection of other trisomies can detect a large portion of these anomalies. These protocols have lower sensitivities (60%) and higher specificities (99%), but similar positive predictive values or rates of false positives, compared with protocols for trisomy 21 screening, because these conditions are much more rare ²⁴.

A new technology, noninvasive prenatal diagnosis, offers the possibility of screening for aneuploidies and other conditions by identifying fragments of fetal DNA in maternal circulation. Early studies have shown a sensitivity for Down syndrome of 100% and a specificity of 99.3% ²⁷. Currently, cost is high and insurance coverage variable, but this may represent an emerging step in sequential genetic testing.

Other genetic screening should be based on the family histories of the patient and her partner. Genetic risk considerations include cystic fibrosis in whites; Tay-Sachs disease in Ashkenazi Jews, Cajuns, and French Canadians; Canavan disease in Ashkenazi Jews; sickle cell disease in Africans; and thalassemias in Africans, East Indians, Hispanics, Mediterraneans, Middle Easterners, and Southeast Asians ¹³.

Neural tube defects affect 1.5 per 1,000 pregnancies and can be detected by testing maternal serum α-fetoprotein levels (sensitivity = 85.7%, specificity = 97.6%) ¹³. Folic acid supplementation should be recommended early, preferably before conception ¹³. Folic acid, 400 mcg daily, started before pregnancy and continued until six to 12 weeks’ gestation reduces the rate of neural tube defects by nearly 75% ¹³. Women taking folic acid antagonists or who have a history of carrying a fetus with a neural tube defect should take 4 mg of folic acid daily ²⁸.

Thyroid Testing

Thyroid-stimulating hormone levels should be measured in women with a history of thyroid disease or symptoms of disease in pregnancy, although there is no evidence that universal testing during pregnancy improves outcomes ²⁹. There is concern that subclinical hypothyroidism in pregnant women may increase the risk of neurodevelopmental delays in infants, but the effectiveness of levothyroxine therapy has not been demonstrated ³⁰. A large randomized trial comparing thyroid-stimulating hormone measurement before 16 weeks’ gestation and after birth found no differences in children’s IQ scores at three years of age ³¹. If the thyroid-stimulating hormone level is abnormal, a free thyroxine test may be useful.

Women with overt hypothyroidism, which complicates one to three per 1,000 pregnancies, are at increased risk of pregnancy loss, preeclampsia, low birth weight, and fetal demise or stillbirth. Hyperthyroidism occurs in two per 1,000 pregnancies and is associated with pregnancy loss, preeclampsia, low birth weight, thyroid storm, prematurity, and congestive heart failure ²⁹.

Infectious Diseases

BACTERIAL VAGINOSIS

Universal screening for bacterial vaginosis is not supported by current evidence. A recent systematic review found that screening and subsequent treatment of infection does not prevent delivery before 37 weeks’ gestation, but decreases the risk of low birth weight and premature rupture of membranes ³².

RUBELLA

Women should be screened for rubella immunity during the first prenatal visit, ideally before conception when vaccination is safe. All women who are nonimmune should be offered vaccination postpartum to prevent congenital rubella syndrome in subsequent pregnancies. Vaccination should not be given during pregnancy, but may be given during lactation ¹³.

VARICELLA

Maternal varicella (chickenpox) can have significant fetal effects, including congenital varicella syndrome (low birth weight and limb, ophthalmologic, and neurologic abnormalities) and neonatal varicella; infection can occur from approximately five days before to two days after birth. Maternal shingles is not a risk for the infant because of passive maternal immunity. There is some evidence to support assessing the mother’s varicella history at the first prenatal visit, with serologic testing for those with a negative history. Women who test negative for immunoglobulin G should avoid exposure to varicella during pregnancy and be offered vaccination postpartum ³³. After a significant exposure, varicella-zoster immune globulin therapy may be considered if available ³⁴.

ASYMPTOMATIC BACTERIURIA

Asymptomatic bacteriuria complicates 2% to 7% of pregnancies. All pregnant women should be screened between 11 and 16 weeks’ gestation and treated, if positive, to reduce the risk of recurrent urinary tract infection, pyelonephritis, and preterm labor ³⁵.

INFLUENZA

Physicians should recommend that all pregnant women receive vaccination for influenza. Pregnant women may be at higher risk of influenza complications than the general population ³⁶. Household contacts of pregnant women should also be offered vaccination.

TETANUS AND PERTUSSIS

Women should receive a diphtheria, tetanus, and pertussis (Tdap) vaccine during each pregnancy. The best time for vaccination is between 27 and 36 weeks’ gestation for antibody response and passive immunity to the fetus; however, the vaccine may be given any time during pregnancy.

GROUP B STREPTOCOCCUS

Group B streptococcus causes significant neonatal morbidity and mortality, particularly among premature infants, and all pregnant women should be offered screening.9,11,41 Increased screening at 35 to 37 weeks’ gestation and treatment with intrapartum antibiotic prophylaxis (penicillin, or clindamycin if allergic) for those who are positive (10% to 30%) have decreased neonatal mortality in the past decade ³⁷. Intrapartum treatment is also recommended for women with group B streptococcus bacteriuria occurring at any stage of pregnancy, and for women with unknown group B streptococcus status and risk factors (e.g., preterm birth before 37 weeks’ gestation, rupture of membranes more than 18 hours before delivery, or intrapartum fever), and for women with a history of group B streptococcus bacteriuria during pregnancy ³⁷.

SEXUALLY TRANSMITTED INFECTIONS

Many sexually transmitted infections can affect a fetus, warranting routine screening in pregnancy. Table 5 summarizes sexually transmitted infections in pregnancy.

Table 5. Sexually Transmitted Infections During Pregnancy

Infection	Testing	Treatment	Complications/risks
Chlamydia	Universal (Centers for Disease Control and Prevention)	Azithromycin (Zithromax), erythromycin, amoxicillin, clindamycin	Congenital eye infections and pneumonia, preterm birth
	Targeted (U.S. Preventive Services Task Force)
Condylomata	Screening not indicated, diagnosis is clinical	Consider cryotherapy or trichloroacetic acid	Vertical transmission, self-limited and usually minor; treatment may not affect transmission
Gonorrhea	Based on personal or geographic risk	Ceftriaxone (Rocephin)	Chorioamnionitis, preterm birth, low birth weight, congenital eye infections
Hepatitis B	Universal	Active and passive immunization of the infant	Vertical transmission
Herpes	Screening not indicated	Acyclovir (Zovirax) or famciclovir (Famvir) prophylaxis starting at 36 weeks’ gestation for women with a history of herpes infection	Vertical transmission (consider cesarean delivery for women with active lesions at delivery)
	Consider culture or polymerase chain reaction testing of lesions
Human immunodeficiency virus	Universal (patient may opt out)	Antiretroviral therapy	Vertical transmission
	Consider repeat screening in the third trimester
Syphilis	Universal rapid plasma reagin or Venereal Disease Research Laboratories testing	Penicillin G benzathine	Congenital syphilis
	Consider repeat testing at 28 weeks’ gestation
Trichomonas	Screening not indicated	Metronidazole (Flagyl)	Preterm birth, premature rupture of membranes, low birth weight

Footnote: It is important for physicians to be familiar with laws and recommendations in their state and community. Many states mandate testing for some sexually transmitted infections at prespecified times during pregnancy. Prevalence of sexually transmitted infections in a geographic area confers independent risk and may be grounds for universal screening in practice or by law.

[Source ² ]

OTHER INFECTIONS

Routine screening for other infections, including toxoplasmosis, cytomegalovirus, and parvovirus, is not recommended during pregnancy.47 Women should be counseled on decreasing risk of exposure to parvovirus B19, and antibody testing should be considered if there is a significant exposure.48
Psychosocial Issues

DOMESTIC VIOLENCE

Domestic violence during pregnancy increases the risk of complications, such as spontaneous abortion, placental abruption, premature rupture of membranes, low birth weight, and prematurity ³⁸. Domestic violence–related homicide is the leading cause of death among pregnant women in the United States ³⁸.

The U.S. Preventive Services Task Force (USPSTF) recommends that clinicians screen women of childbearing age for intimate partner violence, such as domestic violence, and provide intervention services or a referral if a woman screens positive ³⁹. Family physicians should be aware of the signs of abuse in pregnant women, the effect of violence on health, and the increased risk of child abuse after delivery ⁴⁰.

DEPRESSION SCREENING

The American College of Obstetricians and Gynecologists (ACOG) supports depression screening during pregnancy ⁴¹. Perinatal depression is underdiagnosed and complicates 10% to 15% of pregnancies, resulting in significant morbidity for the mother and infant. Complications include prematurity, low birth weight, neurodevelopmental delays, and issues with maternal/infant bonding.

A number of screening tools are available with similar validity and sensitivity. Untreated depression may result in poor prenatal care; inadequate nutrition; and increased alcohol, drug, and tobacco use ⁴².

Complications of Pregnancy

GESTATIONAL DIABETES

Gestational diabetes complicates 2% to 5% of pregnancies and is associated with hypertensive disorders, macrosomia, shoulder dystocia, and cesarean deliveries ⁴³. In addition, the increasing prevalence of undiagnosed type 2 diabetes mellitus and insulin resistance in the general population means many women will first show signs of diabetes during pregnancy. Screening protocols, diagnostic criteria, and treatment criteria are controversial, but diagnosing diabetes earlier in pregnancy and decreasing hyperglycemia improves some pregnancy outcomes ⁴⁴. ACOG, in collaboration with the USPSTF, recommends screening for overt diabetes early in pregnancy in those who are at risk (i.e., previous history of gestational diabetes, obesity, or known glucose intolerance) using HbA1C or fasting blood glucose levels, and screening in all pregnant women at 24 to 28 weeks’ gestation with a 50-g glucose load. An abnormal one-hour test result should be followed by confirmatory testing with a three-hour glucose tolerance test. In contrast, the National Institute for Health and Clinical Excellence has found insufficient evidence to recommend for or against screening for gestational diabetes. In the United States, most women are screened one hour after a 50-g glucose challenge ⁴⁵. Selective screening has been shown to miss gestational diabetes in up to one-half of women.

HYPERTENSION IN PREGNANCY

Blood pressure is generally monitored at each prenatal visit, and women should be counseled on warning signs of preeclampsia. For women who had chronic or severe hypertension in a previous pregnancy, baseline urine protein and preeclampsia laboratory testing may be helpful ⁴⁶. Preeclampsia in a previous pregnancy, chronic hypertension, and low dietary calcium (less than 700 mg) increase the risk of preeclampsia. Calcium supplementation for women with low dietary calcium reduces the risk of preeclampsia by 30% to 50% ⁴⁷. Low-dose aspirin from 12 to 36 weeks’ gestation reduces preeclampsia by 20% in women with a history of preeclampsia, chronic hypertension, diabetes, autoimmune disease, or renal disease, or in women with current gestational hypertension ⁴⁸.

PRETERM BIRTH

Preterm birth (before 37 weeks’ gestation) is a significant cause of neonatal morbidity and mortality, with more than 500,000 preterm births annually in the United States ⁴⁹. Progesterone (preferably weekly injections administered from 16 to 37 weeks’ gestation; daily vaginal suppositories are an alternative) reduces preterm birth by approximately 35% in women with a history of spontaneous preterm labor or premature rupture of membranes ⁵⁰. Cervical cerclage may reduce the risk of preterm birth in women with a previous preterm birth and a short cervix, although the evidence is mixed ⁵¹. Recent studies have shown a significant reduction in preterm birth with vaginal progesterone among women with an asymptomatic short cervix identified on ultrasonography ⁵². Smoking cessation and treatment of genital infections may also reduce the risk of preterm birth.

POSTTERM PREGNANCY

A Cochrane review of induction at 41 weeks’ gestation versus expectant management to 42 weeks’ gestation concluded that perinatal death was less common among women induced at 41 weeks, although it was rare in both groups ⁵³. The rate of perinatal death was 1.7 per 1,000 in the expectant management group versus 0.5 per 1,000 in the induction group (the number needed to treat with induction to prevent one perinatal death was 410 women) ⁵³. The rate of meconium aspiration syndrome and cesarean delivery were lower with induction. Operative vaginal delivery was slightly more common among women induced at 41 weeks. Women should be counseled about the risks and benefits of both approaches.

Although there is no evidence that prenatal testing decreases perinatal death with postterm pregnancy, the standard of care is twice-weekly nonstress testing and weekly assessment of amniotic fluid volume beginning at 41 weeks’ gestation ¹³. Physicians should recommend induction of labor for oligohydramnios (amniotic fluid index less than 5 mL or maximum vertical pocket less than 2 cm at term). A nonreactive, nonstress test is usually followed by a biophysical profile, a contraction stress test, or umbilical artery Doppler ⁵⁴. If these tests are not reassuring after 41 weeks’ gestation, physicians should recommend induction of labor ⁴³.

How can you care for yourself at home?

• Get plenty of rest.
• Exercise every day, if your doctor says it is okay. If you have not exercised in the past, start out slowly. Take many short walks each day.
• Eat a balanced diet. Make sure your diet includes plenty of beans, peas, and leafy green vegetables.
• Drink plenty of fluids, enough so that your urine is light yellow or clear like water. Drink water. Cut down on drinks with caffeine, such as coffee, tea, and cola. If you have kidney, heart, or liver disease and have to limit fluids, talk with your doctor before you increase the amount of fluids you drink.
• Avoid tobacco smoke, alcohol and drugs, chemical fumes, paint fumes, and poisons. Do not smoke or use tobacco. If you need help quitting, talk to your doctor about stop-smoking programs and medicines. These can increase your chances of quitting for good.
• Review all of your medicines with your doctor. Some of your routine medicines may need to be changed to protect your baby. Do not stop or start taking any medicines without talking to your doctor first.

5 Tips to reduce the risk of birth defects

Not all birth defects can be prevented. But you can increase your chances of having a healthy baby by managing health conditions and by adopting healthy behaviors before and during pregnancy.

Taking care of yourself and doing what’s best for you is also best for your baby.

1. Be sure to take 400 micrograms (mcg) of folic acid every day.

Folic acid is important because it can help prevent some major birth defects of the baby’s brain and spine. These birth defects develop very early during pregnancy when the neural tube—which forms the early brain and the spinal cord—does not close properly. You need to start taking folic acid at least one month before becoming pregnant and continue during pregnancy.

In addition to eating foods with natural folate, you can:

• Take a vitamin that has folic acid in it every day.
• Most vitamins sold in the United States have the recommended amount of folic acid women need each day. Check the label on the bottle to be sure it contains 100% of the daily value (DV) of folic acid, which is 400 mcg.
• Eat fortified foods.
• You can find folic acid in some breads, breakfast cereals, and corn masa flour.
• Be sure to check the nutrient facts label and look for one that has “100%” next to folic acid.

2. Book a visit with your healthcare provider before stopping or starting any medicine.

Many women need to take medicine to stay healthy during pregnancy. If you are planning to become pregnant, discuss your current medicines with a healthcare provider, such as your doctor or pharmacist. Creating a treatment plan for your health condition before you are pregnant can help keep you and your developing baby healthy.

3. Become up-to-date with all vaccines, including the flu shot.

Vaccines help protect you and your developing baby against serious diseases. Get a flu shot and whooping cough vaccine (also called Tdap) during each pregnancy to help protect yourself and your baby.

• Flu: You can get the flu shot before or during each pregnancy.
• Whooping Cough: You can get the whooping cough vaccine in the last three months of each pregnancy.

4. Before you get pregnant, try to reach a healthy weight.

Obesity increases the risk for several serious birth defects and other pregnancy complications. If you are underweight, overweight, or have obesity, talk with your healthcare provider about ways to reach and maintain a healthy weight before you get pregnant. Focus on a lifestyle that includes healthy eating and regular physical activity.

5. Boost your health by avoiding harmful substances during pregnancy, such as alcohol, tobacco, and other drugs.

Alcohol: There is no known safe amount of alcohol during pregnancy or when trying to get pregnant. Alcohol can cause problems for a developing baby throughout pregnancy, so it’s important to stop drinking alcohol when you start trying to get pregnant.

Tobacco: Smoking causes cancer, heart disease, and other major health problems. Smoking during pregnancy can also harm the developing baby and can cause certain birth defects. Quitting smoking will help you feel better and provide a healthier environment for your baby.

Other Drugs: Using certain drugs during pregnancy can cause health problems for a woman and her developing baby. If you are pregnant or trying to get pregnant and can’t stop using drugs―get help! A healthcare provider can help you with counseling, treatment, and other support services.

1. American Academy of Pediatrics, American College of Obstetricians and Gynecologist. Guidelines for perinatal care. 8th ed. Elk Grove Village (IL): AAP; Washington, DC: American College of Obstetricians and Gynecologists; 2017[↩][↩]
2. Update on Prenatal Care. Am Fam Physician. 2014 Feb 1;89(3):199-208. https://www.aafp.org/afp/2014/0201/p199.html[↩][↩][↩][↩]
3. Mathews TJ, MacDorman MF. Infant Mortality Statistics from the 2005 Period Linked Birth/Infant Death Data Set National Vital Statistics Reports, Vol. 57, No. 2, July 30, 2008[↩]
4. Roberts JM, Hubel CA. The two stage model of preeclampsia: variations on the theme. Placenta. 2009 Mar;30 Suppl A:S32-7[↩]
5. Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Mathews TJ, Kirmeyer S, Osterman MJK. Births: Final data for 2008. National vital statistics reports; vol 59 no. 1. Hyattsville, MD: National Center for Health Statistics. 2010[↩]
6. Callaghan WM, MacDorman MF, Rasmussen SA, Qin C, Lackritz E. The contribution of preterm birth to infant mortality rates in the United States. Pediatrics 2006;118:1566-1573.[↩]
7. Wang ML, Dorer DJ, Fleming MP, Catlin EA. Clinical outcomes of near–term infants. Pediatrics 2004;114:372–6.[↩]
8. Honein MA, Kirby RS, Meyer RE, Xing J, Skerrette NI, Yuskiv N, et al. The association between major birth defects and preterm birth. Mat Child health J. 2009; 13:164-175.[↩]
9. Behrman RE, Butler AS. (Eds) (2007) Preterm Birth. Causes, Consequences and Prevention. Washington, DC National Academies
   Press.[↩]
10. Ratcliffe SD, et al. Family Medicine Obstetrics. 3rd ed. Philadelphia, Pa.: Mosby Elsevier; 2008.[↩]
11. American College of Obstetricians and Gynecologists. Cervical cytology screening. Obstet Gynecol. 2009;114(6):1409–1420[↩]
12. Lee SJ, Thomas J. Antenatal breast examination for promoting breast-feeding. Cochrane Database Syst Rev. 2008;(3):CD006064[↩]
13. Antenatal care for uncomplicated pregnancies. https://www.nice.org.uk/guidance/CG62[↩][↩][↩][↩][↩][↩][↩][↩][↩][↩][↩][↩][↩][↩][↩]
14. Thornton YS, Smarkola C, Kopacz SM, et al. Perinatal outcomes in nutritionally monitored obese pregnant women. J Natl Med Assoc. 2009;101(6):569–577[↩]
15. Michalowicz BS, et al. Treatment of periodontal disease and the risk of preterm birth. N Engl J Med. 2006;355(18):1885–1894.[↩]
16. Chard T. Pregnancy tests: a review. Hum Reprod. 1992;7(5):701–710.[↩][↩]
17. Demianczuk NN, Van Den Hof MC, Farquharson D, et al.; Diagnostic Imaging Committee of the Executive and Council of the Society of Obstetricians and Gynecologists of Canada. The use of first trimester ultrasound. J Obstet Gynaecol Can. 2003;25(10):864–875.[↩]
18. Whitworth M, Bricker L, Neilson JP, et al. Ultrasound for fetal assessment in early pregnancy. Cochrane Database Syst Rev. 2010;(4):CD007058.[↩][↩]
19. Ewigman BG, Crane JP, Frigoletto FD, et al. Effect of prenatal ultrasound screening on perinatal outcome. N Engl J Med. 1993;329(12):821–827.[↩]
20. American College of Obstetricians and Gynecologists. Management of alloimmunization during pregnancy. Obstet Gynecol. 2006;108(2):457–464.[↩][↩]
21. American College of Obstetricians and Gynecologists. Anemia in pregnancy. Obstet Gynecol. 2008;112(1):201–207[↩]
22. Routine iron supplementation during pregnancy. Review article. U.S. Preventive Services Task Force. JAMA. 1993;270(23):2848–2854.[↩]
23. Haider BA, et al. Multiple-micronutrient supplementation for women during pregnancy. Cochrane Database Syst Rev. 2006;(4):CD004905.[↩]
24. Chitayat D, Langlois S, Wilson RD; Genetics Committee of the Society of Obstetricians and Gynaecologists of Canada; Prenatal Diagnosis Committee of the Canadian College of Medical Geneticists. Prenatal screening for fetal aneuploidy in singleton pregnancies. J Obstet Gynaecol Can. 2011;33(7):736–750.[↩][↩][↩][↩]
25. Smith DK, Shaw RW, Marteau TM. Informed consent to undergo serum screening for Down’s syndrome: the gap between policy and practice. BMJ. 1994;309(6957):776.[↩]
26. Chitayat D, Langlois S, Wilson RD; Genetics Committee of the Society of Obstetricians and Gynaecologists of Canada; Prenatal Diagnosis Committee of the Canadian College of Medical Geneticists. Prenatal screening for fetal aneuploidy in singleton pregnancies. J Obstet Gynaecol Can. 2011;33(7):741.[↩]
27. Verweij EJ, van den Oever JM, de Boer MA, et al. Diagnostic accuracy of noninvasive detection of fetal trisomy 21 in maternal blood. Fetal Diagn Ther. 2012;31(2):81–86.[↩]
28. Wilson RD, Davies G, Désilets V, et al.; Genetics Committee and Executive and Council of the Society of Obstetricians and Gynaecologists of Canada. The use of folic acid for the prevention of neural tube defects and other congenital anomalies. J Obstet Gynaecol Can. 2003;25(11):959–973.[↩]
29. Casey BM, Leveno KJ. Thyroid disease in pregnancy. Obstet Gynecol. 2006;108(5):1283–1292[↩][↩]
30. Surks MI, Ortiz E, Daniels GH, et al. Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA. 2004;291(2):228–238.[↩]
31. Lazarus JH, Bestwick JP, Channon S, et al. Antenatal thyroid screening and childhood cognitive function [published correction appears in N Engl J Med. 2012;366(17):1650]. N Engl J Med. 2012;366(6):493–501.[↩]
32. McDonald HM, Brocklehurst P, Gordon A. Antibiotics for treating bacterial vaginosis in pregnancy. Cochrane Database Syst Rev. 2007;(1):CD000262.[↩]
33. Chickenpox in Pregnancy (Green-top Guideline No. 13). https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg13/[↩]
34. Manual for the Surveillance of Vaccine-Preventable Diseases. 5th ed. Atlanta, Ga.: Centers for Disease Control and Prevention; 2012[↩]
35. Smaill F, Vazquez JC. Antibiotics for asymptomatic bacteriuria in pregnancy. Cochrane Database Syst Rev. 2007;(2):CD000490.[↩]
36. Prevention and control of influenza. MMWR Recomm Rep. 1999;48(RR-4):1–28.[↩]
37. Verani JR, McGee L, Schrag SJ; Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention. Prevention of perinatal group B streptococcal disease—revised guidelines from CDC, 2010. MMWR Recomm Rep. 2010;59(RR-10):1–36[↩][↩]
38. Plichta SB. Intimate partner violence and physical health consequences. J Interpers Violence. 2004;19(11):1296–1323.[↩][↩]
39. https://www.uspreventiveservicestaskforce.org/BrowseRec/Index/browse-recommendations[↩]
40. Zolotor AJ, Theodore AD, Coyne-Beasley T, et al. Intimate partner violence and child maltreatment. Brief Treat Crisis Interv. 2007;7(4):305–321.[↩]
41. American College of Obstetricians and Gynecologists. Screening for depression during and after pregnancy. Obstet Gynecol. 2010;115(2 pt 1):394–395.[↩]
42. American College of Obstetricians and Gynecologists. Use of psychiatric medications during pregnancy and lactation. Obstet Gynecol. 2008;111(4):1001–1020.[↩]
43. Ratcliffe SD, et al. Family Medicine Obstetrics. 3rd ed. Philadelphia, Pa.: Mosby Elsevier; 2008[↩][↩]
44. Metzger BE, Lowe LP, Dyer AR, et al. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. 2008;358(19):1991–2002[↩]
45. Wilkins-Haug L, Horton JA, Cruess DF, et al. Antepartum screening in the office-based practice. Obstet Gynecol. 1996;88(4 pt 1):483–489.[↩]
46. Report of the American College of Obstetricians and Gynecologists’ Task Force on Hypertension in Pregnancy. Obstet Gynecol. 2013;122(5):1122–1131.[↩]
47. Hofmeyr GJ, Lawrie TA, Atallah AN, et al. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2010;(8):CD001059.[↩]
48. Duley L, Henderson-Smart DJ, Meher S, et al. Antiplatelet agents for preventing pre-eclampsia and its complications. Cochrane Database Syst Rev. 2007;(2):CD004659[↩]
49. Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2007. Natl Vital Stat Rep. 2009;57(12):1–23.[↩]
50. Dodd JM, Flenady V, Cincotta R, et al. Prenatal administration of progesterone for preventing preterm birth. Cochrane Database Syst Rev. 2006;(1):CD004947[↩]
51. Berghella V, Odibo AO, To MS, et al. Cerclage for short cervix on ultrasonography. Obstet Gynecol. 2005;106(1):181–189[↩]
52. Romero R, Nicolaides K, Conde-Agudelo A, et al. Vaginal progesterone in women with an asymptomatic sonographic short cervix in the midtrimester decreases preterm delivery and neonatal morbidity. Am J Obstet Gynecol. 2012;206(2):124.e1–19[↩]
53. Gülmezoglu AM, Crowther CA, Middleton P, et al. Induction of labour for improving birth outcomes for women at or beyond term. Cochrane Database Syst Rev. 2012;(6):CD004945[↩][↩]
54. American College of Obstetricians and Gynecologists. Management of postterm pregnancy. Obstet Gynecol. 2004;104(3):639–646.[↩]