GENERAL PREVENTION

In the United States, the typical prenatal visit schedule consists of monthly visits for weeks 4 to 28 of pregnancy, visits twice monthly from 28 to 36 weeks, weekly after week 36 (until delivery, typically at weeks 38 to 41).

HISTORY

Collect the following histories in the initial prenatal visit and continually update throughout the pregnancy (1),(2):

• Medical history, with an emphasis on the following but not limited to prediabetes/DM, obesity/overweight, thyroid disorders, pregestational hypertension (HTN) or history of hypertensive disease in pregnancy (e.g., chronic HTN, gestational HTN, pre-eclampsia with or without severe features, HELLP syndrome), maternal age at delivery, previous DVT/PE, known uterine anomaly, autoimmune disease (e.g., systemic lupus erythematosus, rheumatoid arthritis, Sjögren), strong family history of diseases in pregnancy or congenital/inheritable conditions
• Obstetrical history, including but not limited to:
  • History of preterm delivery or PTL
  • History of hypertensive disease in pregnancy
  • History of gestational diabetes (GDM) or early onset GDM
  • Other medical conditions raising maternal risk: HIV/AIDS or other STIs in the past, sickle cell disease, intrahepatic cholestasis of pregnancy
  • Personal history of delivering a newborn with birth defects/trisomies or congenital/inheritable condition
• Psychosocial history, including but not limited to:
  • Depression screening (use EPDS or PHQ-9), intimate partner violence (ACOG guidelines: Screen all pregnant patients at the first prenatal visit, 1x/trimester, and at postpartum checkup.)
  • Tobacco, alcohol, and drug use
  • Lifestyle, nutrition, toxin exposures, travel to areas with endemic diseases, stressors/supports; potential barriers to care (preferred language, housing, transportation, child care issues, economic constraints, work schedule)

PHYSICAL EXAM

• A full physical exam on intake (1),(2)
• At each subsequent prenatal visit, the following should be recorded (1),(2):
  • Weight gain recommendations (2009 IOM)
    • BMI <18.5 kg/m² (underweight): 28 to 40 lb (12.5 to 18 kg)
    • BMI 18.5 to 24.9 kg/m² (normal weight): 25 to 35 lb (11.5 to 16 kg)
    • BMI 25 to 29.9 kg/m² (overweight): 15 to 25 lb (7 to 11.5 kg)
    • BMI ≥30 kg/m² (obese): 11 to 20 lb (5 to 9 kg)
  • BP (mm Hg): Assess for mild (≥140 to <160/≥90 to <110) or severe range (≥160/≥110) BP if not normal
  • Fundal height: Start after weeks 20 to 24.
  • Fetal heart rate: usually audible by 8 to 12 weeks’ GA with a Doppler device
  • Pelvic/cervical exam if indicated
  • Fetal position by Leopold maneuver at weeks 32 to 36; confirm by ultrasound (US) if available.

DIAGNOSTIC TESTS & INTERPRETATION

• First prenatal visit (1):
  • Lab tests
    • Hematocrit or hemoglobin, blood type, Rhesus type, and antibody screen
    • Hemoglobin electrophoresis: Screen for sickle cell disease, SCT, or thalassemia.
    • Urine culture
    • Ab titers for Rubella and Varicella
    • STI screen: RPR/VDRL, GC/C, hepatitis B, HIV
    • Not recommended: routine screening for bacterial vaginosis, toxoplasmosis, CMV, and parvovirus; thyroid and vitamin D deficiency
  • Carrier screening (including, but not limited to):
    • Cystic fibrosis screening: Counseling is needed first, and screening should be offered when one partner is of Caucasian, European, or Ashkenazi Jewish descent.
    • Spinal muscular atrophy
    • Hemoglobinopathies (i.e., risk for sickle cell disease, thalassemia)
  • Screening for fetal aneuploidy:
    • Counseling should be provided before any shared decision-making on testing.
    • All women should be offered screening or diagnostic testing, regardless of maternal age.
    • 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), quadruple test: α-fetoprotein (AFP), unconjugated estriol (UE3), hCG, dimeric inhibin-A (DIA)
    • Cell-free DNA testing: should not be used as a substitute for diagnostic testing due to potential for false-positive or false-negative results; all women with positive screening test should have a diagnostic procedure before any irreversible action is taken.
    • 1st-trimester “combined test” between 11 and 13 weeks’ GA using both NT and hCG/PAPP-A blood testing is an effective protocol; 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.)
    • Women who undergo 1st-trimester screening should be offered 2nd-trimester assessment for open fetal defects and US screening for other fetal structural defects.
    • 2nd-trimester screening: Obtain quadruple test ideally at weeks 15 to 18 but can be done as late as week 22.
    • If risk is found, all pregnant women should be offered invasive prenatal diagnostic testing regardless of maternal age or other risk factors (3); diagnostic tests for genetic disorders:
      • CVS: 1st trimester: usually done weeks 10 to 12; small sample of the placenta; chorionic tissue sample obtained either transcervical (TC) or transabdominal (TA)
      • Amniocentesis: usually done weeks 15 to 18; small sample of amniotic fluid from the amniotic sac surrounding the developing fetus is obtained by a US-guided TA approach.
      • The rate of procedure-related pregnancy loss that is attributable to a prenatal diagnostic procedure is 0.1–0.3% when performed by experienced health care providers (3).
      • Chromosomal microarray analysis: can detect a pathogenic copy number variant in about 1.7% of patients with normal US and normal karyotype; make available to any patient choosing to undergo invasive diagnostic testing; primary test for patients undergoing diagnostic testing for indication of a fetal structural abnormality detected by US examination (3)
  • Cervical cancer screening:
    • A Pap smear or approved high-risk HPV screen should be obtained when indicated by standard Pap screening guidelines, regardless of gestation, to start at age 21 years.
    • Squamous intraepithelial lesions can progress during pregnancy but often regress postpartum.
    • LSIL/CIN1 in pregnancy: Colposcopy is preferred, but it is acceptable to defer colposcopy to 6 weeks postpartum.
    • CIN 2 or CIN 3 in pregnancy: In the absence of invasive disease or advanced pregnancy, additional colposcopic and cytologic examinations are acceptable; repeat biopsy is recommended only if appearance of lesion worsens or if cytology suggests invasive cancer; it is acceptable to defer reevaluation until 6 weeks postpartum.
    • Endocervical sampling is contraindicated in pregnancy.
• Subsequent prenatal visits (1),(2):
  • Urinalysis for glucose and protein: limited evidence for benefit or harm; the baseline during initial intake may be useful for high-risk patients (e.g., chronic HTN).
• 24- to 28-week prenatal visits (1),(2):
  • Obtain diabetes screen.
  • Repeat hematocrit or hemoglobin, and repeat antibody screen in Rh-negative mother prior to receiving prophylactic Rh immunoglobulin. Repeat syphilis testing in the 3rd trimester around 28 weeks in all cases (2018 CDC, ACOG and AAP guidelines due to rising cases of congenital syphilis). Retest for HIV at 28 weeks in high-risk cases. Retest for syphilis and HIV at delivery in high-risk cases.
  • GDM screening (2)
    • The ADA and ACOG define increased risk of diabetes in pregnancy who need earlier screening based on BMI ≥25 kg/m² (≥23 kg/m² in Asian Americans) plus one or more of the following:
      • Previous pregnancy history of GDM, fetal macrosomia (≥4,000 g BW prior delivery), or stillbirth
      • HTN (140/90 mm Hg or being treated for HTN)
      • HDL cholesterol ≤35 mg/dL (0.90 mmol/L)
      • Fasting triglyceride ≥250 mg/dL (2.82 mmol/L)
      • Hemoglobin A1C ≥5.7%, impaired glucose tolerance or impaired fasting glucose
      • PCOS, acanthosis nigricans, nonalcoholic steatohepatitis, morbid obesity prepregnancy BMI ≥40 kg/m², and other conditions associated with insulin resistance
      • Current or past history of cardiovascular disease
      • Family history of diabetes—first-degree relative (parent or sibling)
      • High-risk ethnicity or communities
    • Early onset diagnosis is made via 2-step testing (see below) ideally between weeks 12 to 16 of pregnancy for at risk cases.
    • For typical low-risk cases, employ 2-step testing starting week 24 to 28: Screen using a 1-hour glucola test and, if needed and appropriate (see below*), a 3-hour diagnostic test.
    • The risk of developing type 2 diabetes with the personal history of GDM is up to 50% in the next 20 years after delivery. Therefore, a fasting 75-g 2-hour oral glucose tolerance test (OGTT), because it is only 1 step, may be helpful in diagnosing postpartum diabetes or glucose intolerance. It is unclear if the 75-g 2-hour GTT is comparable to the 2-step approach in diagnosing GDM*.
    • Assess for readiness for change in diet +/− exercise. Provide counseling, nutrition, and other support on diagnosis of GDM. Continue to support during the postpartum period and beyond.
    • Diagnosing GDM (ACOG and AAFP guidelines):
      • Setting cutoff for “elevated 1-hour GCT”: Setting the cutoff at 130 or 135 may be prudent for a practice with higher local prevalence of GDM. Setting the cutoff at 140 may be prudent for a practice with low local prevalence of GDM.
      • Routine screening for GDM (~week 24 to 28): 50 g PO nonfasting glucose load with blood glucose testing 1 hour later; if elevated, then proceed to 3-hour testing for diagnosis.
        • *Each practice or institution may have internal guidelines for 1-hour results if ≥180 to 185 and proceed with fasting BG monitoring instead of proceeding with 3-hour GTT.
      • Diagnostic test: 3-hour GTT is achieved, on a separate day from 1-hour GCT, by 100 g PO glucose load after fasting for ≥8 hours with blood drawn: fasting, 1, 2, and 3 hours after ingestion of glucose. A positive diagnosis of GDM requires that ≥2 positive thresholds by either of the criteria listed below.
        • NDDG standard: ≥105 (fasting), ≥190 (1-hour), ≥165 (2-hour), ≥145 (3-hour)
        • Carpenter and Coustan standard: ≥95 (fasting), ≥180 (1-hour), ≥155 (2-hour), ≥140 (3-hour)
      • ACOG states, due to known adverse events, one elevated value from the 3-hour GTT may be sufficient to demonstrate evidence of glucose intolerance.
      • 1-step approach (75-g OGTT) on all women will increase the diagnosis of GDM, but sufficient prospective studies demonstrating improved outcomes are still lacking and need further research. ACOG does acknowledge that some centers may opt for “1 step” if warranted based on their population.
• 35 to 37 week prenatal visits (1):
  • Group B Streptococcus (GBS) culture: Screen all low-risk cases at 35 to 37 weeks’ GA to identify women colonized with GBS. For cases requiring induction at 37 weeks or earlier, screen as soon as possible.
  • High-risk patients: High-risk patients should be screened again for gonorrhea, chlamydia, syphilis, and HIV.
• Postterm pregnancy:
  • The rate of stillbirth increases with GA by 1/3,000 per week at 41 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’ GA reduced rates of perinatal death without increased rates of cesarean delivery.
  • For prenatal care >41 to 42 weeks, fetal well-being should be assessed with nonstress testing and US assessment of amniotic fluid volume.

ISSUES FOR REFERRAL

Abnormal screening labs or imaging may prompt referral to maternal–fetal medicine specialist or other medical specialists as indicated.

PATIENT EDUCATION

• Immunizations during pregnancy per CDC:
  • Tdap during each pregnancy (should be given between 27 and 36 weeks’ GA); hepatitis B and influenza; likely safe include meningococcal, rabies; contraindicated or safety not established: live vaccines including BCG, MMR, and varicella
  • Vaccination against COVID-19 is recommended in pregnancy. COVID-19 increases the risk for patient and fetus.
• Recommendations for use of dietary supplements in pregnancy (1),(2)
  • Folic acid 0.4 mg/day beginning at least 1 month prior to attempting conception and continuing throughout pregnancy; 1 to 4 mg for women at higher risk of having child with neural tube defect beginning 1 to 3 months before conception, continued through first 12 weeks of gestation, and then reduced to 0.4 mg/day
  • Calcium: 1,000 to 1,300 mg/day; supplement may be beneficial for women with high risk for gestational HTN or communities with low dietary calcium intake.
  • Caffeine: Limit to <200 mg/day; more research needed
  • Iron: Screen for anemia (hemoglobin/hematocrit) and order extra iron supplementation if necessary.
  • Vitamin A: Pregnant women in industrialized countries should limit to <5,000 IU/day.
  • Vitamin D: 200 to 1,200 IU (dose in standard prenatal vitamin) is recommended until more evidence is available to support different dose.
• Other important counseling topics during pregnancy (2):
  • Airline travel: generally safe until up to week 35; >2 hours without ambulation increases the risk of thrombosis.
  • Exercise: Healthy women with uncomplicated pregnancies should continue to exercise.
  • Seat belts/airbags: Wear lap and shoulder seatbelts; working airbags (ACOG and AAFP)
  • Sexual activity: Intercourse while pregnant is not associated with adverse outcomes. Avoiding sex may be necessary in cases of low-lying placenta, placenta previa, or vasa previa.
  • Alcohol, cigarettes, and illicit drugs are injurious to fetal and maternal health.
  • Pregnancy-safe medications (teratogenicity)
  • Avoid large fish such as shark, tuna, swordfish, and mackerel (high levels of mercury).
  • Preconception counseling offers the opportunity to discuss individualized risks.

ICD10

• 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
• Z34.80 Encounter for suprvsn of normal pregnancy, unsp trimester

SNOMED

• 424525001 Antenatal care (regime/therapy)
• 134435003 Routine antenatal care (procedure)
• 17629007 prenatal care education (procedure)
• 243787009 antenatal screening (procedure)
• 312404004 Antenatal blood tests (procedure)
• 424619006 Prenatal visit (regime/therapy)