> Table of Contents > Prenatal Care and Testing
Prenatal Care and Testing
Fozia Akhtar Ali, MD
Teny Anna Philip, MD
image BASICS
  • The goal of prenatal care is to ensure the birth of a healthy baby with minimal risk for the mother by the following:
    • Identifying the patient who is at risk for complications
    • Estimating the gestational age (GA) as accurately as possible
    • Evaluating the health status of mother and fetus
    • Encouraging and empowering the patient to do her part to care for herself and her baby-to-be
    • Intervening when fetal abnormalities are present to prevent morbidity
  • A recommended prenatal care schedule consists of the following:
    • Monthly visits to a health care professional for weeks 4 to 28 of pregnancy
    • Visits twice monthly from 28 to 36 weeks
    • Weekly after week 36 (delivery at week 38 to 40)
  • Recommendations for use of dietary supplements in pregnancy
    • Folic acid supplementation (0.4 to 0.8 mg) prior to conception; 4 mg for secondary prevention
    • Calcium: 1,000 to 1,300 mg/day; supplement may be beneficial for women with high risk for gestational hypertension or communities with low dietary calcium intake.
    • Iron: Screen for anemia (Hgb/Hct) and treat if necessary. Recommend 30 mg/day of iron in pregnant women.
    • Vitamin A: Pregnant women in industrialized countries should limit to <5,000 IU/day.
    • Vitamin D: Consider supplementation in women with limited exposure to sunlight.
  • Routine thyroid screening and vitamin D deficiency during pregnancy is not recommended.
  • A full physical exam should be performed at the first prenatal appointment.
  • At each subsequent prenatal visit, the following should be recorded:
    • Weight: Total weight gain range (lb) should be 25 to 35 lb, except in obese women, for whom weight gain should be <15 lb.
    • BP
      • ACOG defines hypertension as BP >140 mm Hg systolic or >90 mm Hg diastolic (1,2).
      • Monitor BP especially closely in patients with chronic hypertension (predating pregnancy), preeclampsia/eclampsia, or gestational hypertension.
    • UA for glucose and protein; 24-hour protein excretion is the gold standard but not practical.
    • Fundal height
    • Fetal heart rate: usually audible by 12 weeks' GA with a Doppler instrument
    • Routine fetal movement counts not recommended
    • Fetal position by abdominal palpation at 36 weeks
    • Pelvic/cervical exam if indicated
Cervical cancer screening
  • A Pap smear should be obtained when indicated by standard Pap screening guidelines, regardless of gestation (ACOG, USPSTF, ASCCP, ACS, and ASCP guidelines state that women <21 years should not be screened regardless of age of sexual initiation or other risk factors).
  • Squamous intraepithelial lesions can progress during pregnancy but often regress postpartum.
  • LSIL in pregnancy: colposcopy preferred, but it is acceptable to defer colposcopy to postpartum (3).
  • Colposcopy only to exclude the presence of invasive cancer in high-risk women
  • Cervical biopsy should be avoided unless a malignancy is suspected. Endocervical sampling is contraindicated.
  • First prenatal visit
    • Lab tests
      • Hematocrit or hemoglobin
      • Blood type: A, B, AB, or O
      • Rhesus type and antibody screen: Rh(+) or Rh(−)
      • Hemoglobin electrophoresis for patients at risk for sickle cell disease or thalassemia
      • Urine testing for glucose and protein
      • Urine culture
      • Rubella titer
      • Syphilis test
      • Gonorrhea/chlamydia screening
      • Hepatitis B surface antigen
      • HIV testing (patient may “opt out” if chooses to decline)
      • Routine screening for bacterial vaginosis, toxoplasmosis, CMV, and parvovirus not recommended
      • Cystic fibrosis screening (information should be made available to all couples)
        • Cystic fibrosis carrier screening should be offered before conception or early in pregnancy when one partner is of Caucasian, European, or Ashkenazi Jewish descent (4).
        • It is reasonable to offer cystic fibrosis carrier screening to all couples regardless of race or ethnicity as an alternative to selective testing.
  • Screening tests (for birth defects), noninvasive
    • US nuchal translucency (NT): measures thickness at the back of the neck of the fetus
    • Blood screens: human chorionic gonadotropin (hCG), pregnancy-associated plasma protein A (PAPP-A), quad screen: &agr;-fetoprotein (AFP), unconjugated estriol (UE3), hCG, inhibin-A (INH-A)
    • Cell-free DNA testing should be offered as an alternative noninvasive method of screening for fetal aneuploidies to high-risk pregnant women between 10 and 22 weeks' gestation. Women who elect cell-free DNA testing will also need an AFP test for neural tube defects. The assay also allows screening for aneuploidy, rhesus typing in Rh(D) -negative women, and single-gene disorders (limited to detection of paternally inherited mutation). Because of a small but real risk for false-positive results, most experts advise using these assays as screening tests and confirming positive result with invasive prenatal diagnostics.
    • 1st-trimester screening between 11 and 14 weeks' GA using both NT and hCG/PAPP-A blood testing is an effective protocol in the general population and is more effective than NT alone, with an 83% detection rate for Down syndrome, with false-positive rate of 5%. Detects trisomy 21 (Down syndrome) and trisomy 18 (Edward syndrome). May be performed either as a single combined stand-alone test (US NT 1 blood [HCG and PAPP-A]) or as part of a sequential “step-by-step” 1st- and 2nd-trimester screening process (see the following discussion)
    • 2nd-trimester screening protocols
      • Obtain “multiple marker”/quad screen between 15 and 21 weeks' GA, optimally between 16 and 18 weeks; ˜84% detection rate for trisomy 21, trisomy 18, and neural tube defects (NTDs), with false-positive rate of 5%, or
      • 2-step integrated screening protocol: combines information collected during the 1st and 2nd trimesters of the pregnancy to determine the risk of Down syndrome, trisomy 18, or open NTD:
        • Two options: stepwise sequential integrated screen (˜91% detection rate with false-positive rate 3.3%):
          • 1st trimester: NT measurement, plus blood (hCG, PAPP-A):
            • If calculated risk for Down syndrome is ≥1:30, then additional steps are recommended (genetic counseling, US, and chorionic villi sampling [CVS]).
            • If calculated risk for Down syndrome is <1:30 then
          • 2nd-trimester quad screen (AFP, UE3, hCG, INH-A) is required, or
        • Serum integrated screen: 88% detection rate with false-positive rate of 4.5%; requires a 1st-trimester PAPP-A blood test without NT measurement, and a 2nd-trimester (16- to 18-week quad screen)
  • Diagnostic tests (for birth defects), invasive
    • ACOG guidelines: All pregnant women, not just women ≥35 years, should be offered invasive prenatal diagnostic testing, such as CVS and amniocentesis to detect possible genetic abnormalities in their fetuses (5)[C].
    • Women found to be at increased risk of having a baby with Down syndrome with 1st-trimester screening should be offered genetic counseling and the option of CVS or midtrimester amniocentesis. If screening tests show increased risk of birth defect, there are two possible diagnostic tests:
      • CVS: 1st trimester: usually done after 10 weeks (10 to 12 weeks). Small sample of the placenta; chorionic tissue sample obtained either transcervical (TC) or transabdominal (TA). Complication: pregnancy loss rate of 1.0-1.5%
      • Amniocentesis
        • 1st trimester: usually at 11 to 13 weeks but higher rate of pregnancy loss and complication than either CVS or early 2nd-trimester procedures; therefore, not recommended
        • P.843

        • 2nd trimester: usually done after 15 weeks (15 to 18 weeks). The prenatal diagnostic technique associated with the lowest risk of pregnancy loss. Small sample of amniotic fluid from the amniotic sac surrounding the developing fetus is obtained by an US-guided TA approach. Complication: pregnancy loss rate of ≤0.5%
  • 24 to 28 weeks
    • Obtain diabetes screen (see the following discussion), repeat hematocrit or hemoglobin, and repeat antibody screen in Rh-negative mother prior to receiving prophylactic Rh immunoglobulin.
      • Gestational diabetes mellitus (GDM) screening: universal recommendation for ideal approach for screening and diagnosis of GDM remains elusive. In 2010, the International Association of Diabetes and Pregnancy Study Group proposed a new system in which diabetes in pregnancy is classified as overt versus gestational diabetes. The American Diabetes Association reaffirmed this in 2010 and 2013. Presently, this system is not endorsed by ACOG because there is no evidence that one-step screening using this criteria leads to clinically significant improvements in maternal and fetal outcomes but would lead to significant increase in health care costs.
      • Overt diabetes (test when women first present for prenatal care): fasting blood sugar ≥126 mg/dL or HbA1c ≥6.5%, or random ≥200 mg/dL that is confirmed with subsequent fasting blood sugar or HbA1c. (These thresholds were chosen due to correlation with adverse vascular events, e.g., retinopathy and CAD.)
      • Gestational diabetes: fasting plasma glucose >92 mg/dL but is <126 mg/dL at any GA. At 24 to 28 weeks of gestation, a 75 g 2-hour oral glucose tolerance test with at least 1 abnormal result: FBG ≥92 mg/dL, but <126 mg/dL or 1-hour ≥180 mg/dL, or 2-hour ≥153 mg/dL
      • The prevalence of gestational diabetes in the United States can be 2-25%, greater in African Americans, Hispanics, Native Americans, and Asians than in Caucasians. Using the IADPSG criteria for overt versus gestational diabetes, ˜18% of women would be diagnosed with diabetes during pregnancy.
      • The following guidelines for GDM are established by ACOG:
        • Specified cutoffs define GDM
          • A value of >130 mg/dL will identify 90% of women with GDM, but 20-25% of all women screened will need to continue to the 3-hour oral glucose tolerance test (OGTT) (1,2).
          • Raising the value to >140 mg/dL will identify only 80% of women with GDM but decrease to 14-18% the number of women who will need to continue to the 3-hour OGTT (6).
        • Screening test: 1-hour OGTT (nonfasting)
          • 50 g PO glucose load with blood glucose testing 1 hour later
          • Carpenter and Coustan positive screen: >130 mg/dL
          • National Diabetes Data Group (NDDG) positive screen: >140 mg/dL
        • Diagnostic test: 3-hour OGTT (fasting)
          • If abnormal 1-hour OGTT screening test, may be followed by a 3-hour OGTT
          • 100 g PO glucose load with blood drawn: fasting, 1, 2, and 3 hours after ingestion of glucose
          • Either the plasma or serum glucose level designated by Carpenter and Coustan or by the NDDG are appropriate to use:
            • *A positive diagnosis of GDM requires that ≥2 thresholds be exceeded.
              • Carpenter and Coustan standard
                • *>95 (fasting), >180 (1-hour), >155 (2-hour), >140 (3-hour)
              • National Diabetes Data Group standard:
                • *105 (fasting), >190 (1-hour), >165 (2-hour), >145 (3-hour)
  • 35 to 37 weeks
    • Group B Streptococcus (GBS) culture: Universal screening for GBS colonization at 35 to 37 weeks of gestation remains the sole strategy for intrapartum antibiotic prophylaxis.
    • High-risk patients: High-risk patients should be screened again for gonorrhea, chlamydia, HIV, and syphilis.
  • Postterm pregnancy
    • Rate of stillbirth increases with GA by 1/3,000 per week at 37 weeks; 3/3,000 per week at 42 weeks; and 6/3,000 at 43 weeks. In one meta-analysis, routine induction of labor at 41 weeks' gestation reduced rates of perinatal death without increased rates of cesarean delivery.
    • For gestational periods beyond 42 weeks, fetal well-being should be assessed with nonstress testing and US assessment of amniotic fluid volume.
Abnormal screening labs or imaging may prompt referral to maternal-fetal medicine specialist or other medical specialist, as indicated.
  • Immunizations during pregnancy. The following vaccines are considered safe per CDC (7):
    • Women should get (Tdap) during each pregnancy. Ideally, the vaccine should be given between 27 and 36 weeks of pregnancy—Hep B, and influenza; possibly include meningococcal, rabies. Contraindicated during pregnancy or safety not established:live vaccines including BCG, MMR, and varicella.
    • Patients should be made aware of the tests that are performed routinely, as well as other tests that might be elected (e.g., CVS or amniocentesis), as well as the choices that would be available if testing were abnormal (pregnancy termination, preparation for the birth of an infant with congenital anomalies, further testing).
  • Prevention
    • Preconception counseling offers the opportunity to discuss individualized risks.
  • To decrease the risks of NTDs, preconception folate supplementation is indicated.
  • Recommendations
    • Airline travel: generally safe until up to 4 weeks from EDD. Lengthy trips associated with increased risk of thrombosis
    • Caffeine: Limit to <200 mg/day. Correlation between IUGR and miscarriage with caffeine is undetermined at this time.
    • Exercise: Healthy women with uncomplicated pregnancies should continue to exercise.
    • Seat belts/air bags: ACOG recommends that pregnant women wear lap and shoulder seatbelts and should not turn off air bags.
    • Sexual activity: Intercourse is not associated with adverse outcomes.
  • Alcohol, cigarettes, and illicit drugs are injurious to fetal and maternal health.
    • Pregnancy-safe medications (teratogenicity)
1. American College of Obstetricians and Gynecologists. Screening tools—domestic violence. http://www.acog.org/ACOG_Departments/Violence_Against_Women/Screening_Tools-Domestic-Violence. Accessed August 7, 2012.
2. Committee on Obstetric Practice. Committee Opinion no. 514: emergent therapy for acute-onset, severe hypertension with preeclampsia or eclampsia. Obstet Gynecol. 2011;118(6):1465-1468.
3. Massad LS, Eienstein MH, Huh WK, et al. 2012 updated consensus guidelines for the management of abnormal cervical cancer screening tests and cancer precursors. J Low Genit Tract Dis. 2013;17(5)(Suppl 1):S1-S27.
4. American College of Obstetricians and Gynecologists Committee on Genetics. ACOG Committee Opinion no. 486: update on carrier screening for cystic fibrosis. Obstet Gynecol. 2011;117(4):1028-1031.
5. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin no. 88, December 2007. Invasive prenatal testing for aneuploidy. Obstet Gynecol. 2007;110(6):1459-1467.
6. Berger H, Crane J, Farine D, et al. Screening for gestational diabetes mellitus [in English, French]. J Obstet Gynaecol Can. 2002;24(11):894-912.
7. Centers for Disease Control and Prevention. GBS prevention guidelines. http://www.cdc.gov/groupbstrep/guidelines/newdifferences.html.2010guidelines
  • Z34.90 Encntr for suprvsn of normal pregnancy, unsp, unsp trimester
  • Z36 Encounter for antenatal screening of mother
  • Z34.00 Encntr for suprvsn of normal first pregnancy, unsp trimester
Clinical Pearls
Prenatal care and screening are best accomplished using standardized flow sheets and checklists to ensure that the complex sequence of evaluations and education is performed consistently and properly.