67.4 Routine Prenatal Care & Longitudinal Pregnancy Management

Prenatal Care as Longitudinal Chronic Care

The blueprint separates acute pregnancy management issues (Acute Care & Diagnosis) from pregnancy management issues as a Chronic Care Management activity. The distinction is deliberate: ectopic pregnancy and miscarriage are episodic problems, while routine prenatal care is a structured 9-month program of scheduled visits, timed laboratory testing, timed immunizations, and timed prophylaxis. The examination tests what is done, and when — gestational-age anchors are the single highest-yield content in this section.

Family medicine remains a maternity care specialty, and even physicians who do not attend deliveries must recognize the schedule to co-manage patients and to identify when a pregnancy has fallen off it.

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The Visit Schedule

The traditional schedule yields roughly 12 to 14 visits for an uncomplicated nulliparous pregnancy:

Reduced-frequency schedules, telehealth-supplemented models, and group prenatal care (CenteringPregnancy) are acceptable alternatives for low-risk patients and are associated with comparable or improved outcomes and higher patient satisfaction. High-risk pregnancies are individualized and seen more often.

Every visit includes: blood pressure, weight, urine dipstick when indicated, fundal height (after ~20 weeks), fetal heart tones (after ~10–12 weeks by Doppler), fetal movement inquiry (third trimester), and presentation assessment near term.

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Dating: Get It Right Once

• Naegele's rule: estimated due date = first day of the last menstrual period − 3 months + 7 days, assuming a regular 28-day cycle.
• First-trimester ultrasound crown-rump length is the most accurate method (± 5–7 days) and should redate the pregnancy when it differs from the LMP by more than 7 days before 14 0/7 weeks.
• Accuracy degrades with advancing gestation; second-trimester biometry is accurate only to ± 10–14 days and third-trimester to ± 21–30 days. A pregnancy is not redated in the third trimester based on size discrepancy alone — that finding raises growth restriction or macrosomia instead.

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First-Visit Laboratory Panel

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The Gestational-Age Timeline

  0 ──── 12 ──── 16 ──── 20 ──── 24 ──── 28 ──── 32 ──── 36 ──── 40 weeks
  │       │       │       │       │       │       │       │
  │       │       │       │       │       │       │       └─ GBS culture 36 0/7 – 37 6/7
  │       │       │       │       │       │       └───────── Maternal RSV (Abrysvo) 32 0/7 – 36 6/7,
  │       │       │       │       │       │                  seasonally September – January
  │       │       │       │       │       └───────────────── Tdap every pregnancy, 27 – 36 weeks
  │       │       │       │       │                          Anti-D immune globulin at 28 weeks
  │       │       │       │       │                          Repeat antibody screen (Rh-negative)
  │       │       │       │       └─────────────────────────  GDM screening 24 – 28 weeks
  │       │       │       └─────────────────────────────────  Anatomy ultrasound 18 – 22 weeks
  │       │       └─────────────────────────────────────────  MSAFP / quad screen 15 – 22 weeks
  │       └─────────────────────────────────────────────────  Low-dose aspirin started 12 – 28 weeks
  │                                                           (ideally before 16 weeks)
  └─────────────────────────────────────────────────────────  Dating US, first-visit labs,
                                                              cfDNA screening from 10 weeks

Aneuploidy screening

Screening must be offered to all pregnant patients regardless of age. Options include cell-free DNA (from 10 weeks; the most sensitive screen for trisomy 21, but still a screen — a positive result requires diagnostic confirmation by chorionic villus sampling at 10–13 weeks or amniocentesis at 15 weeks or later), first-trimester combined screening with nuchal translucency at 11–14 weeks, and the second-trimester quadruple screen at 15–22 weeks. Carrier screening and a discussion of diagnostic testing are offered alongside.

Gestational diabetes screening at 24 to 28 weeks

Patients with obesity, prior gestational diabetes, a first-degree relative with diabetes, prior macrosomic infant, or polycystic ovary syndrome should be screened early (first visit) and rescreened at 24–28 weeks if the early screen is normal.

Rh(D) alloimmunization prophylaxis

For every unsensitized Rh(D)-negative patient: repeat the antibody screen and give anti-D immune globulin 300 µg at 28 weeks, and again within 72 hours of delivery if the newborn is Rh(D) positive. Additional doses follow sensitizing events — miscarriage, ectopic pregnancy, termination, amniocentesis or CVS, external cephalic version, antepartum bleeding, or abdominal trauma.

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Immunizations in Pregnancy

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Preeclampsia Prevention and Recognition

Low-dose aspirin 81 mg daily is a USPSTF Grade B recommendation, started between 12 and 28 weeks — optimally before 16 weeks — and continued until delivery, for patients with one high-risk factor or two or more moderate-risk factors.

• High-risk factors: prior preeclampsia, multifetal gestation, chronic hypertension, pregestational type 1 or 2 diabetes, chronic kidney disease, autoimmune disease (SLE, antiphospholipid syndrome).
• Moderate-risk factors: nulliparity, obesity (BMI > 30), family history of preeclampsia in a mother or sister, age 35 or older, sociodemographic factors, prior adverse pregnancy outcome, and an interpregnancy interval longer than 10 years.

Diagnostic anchors after 20 weeks: gestational hypertension is systolic ≥ 140 or diastolic ≥ 90 mm Hg on two occasions at least 4 hours apart, without proteinuria. Preeclampsia adds proteinuria or, in its absence, thrombocytopenia (< 100,000/µL), serum creatinine > 1.1 mg/dL or doubling, transaminases at twice the upper limit of normal, pulmonary edema, or new-onset headache or visual symptoms. Severe features include BP ≥ 160/110 mm Hg and any of those end-organ findings.

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Nutrition, Weight and Screening

• Folic acid 400–800 µg daily preconception and in the first trimester; 4 mg daily for a prior neuroepithelial defect–affected pregnancy.
• Gestational weight gain (NASEM/IOM ranges by prepregnancy BMI): underweight 28–40 lb, normal weight 25–35 lb, overweight 15–25 lb, obesity 11–20 lb.
• Perinatal depression: USPSTF Grade B for screening pregnant and postpartum patients, and a separate Grade B for referring patients at increased risk to counseling interventions. The Edinburgh Postnatal Depression Scale is the most-used instrument.
• Universal screening for intimate partner violence, substance use (including tobacco, alcohol, cannabis, and opioids), and food and housing insecurity should be built into the schedule.
• Avoid: ACE inhibitors and ARBs, warfarin, isotretinoin, methotrexate, valproate, and live vaccines. Continue most needed chronic medications after risk–benefit review — abrupt discontinuation of antiseizure or psychiatric medication frequently causes more harm than continuation.

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Board Exam Traps

1. LMP-based due date differs by 9 days from a 9-week crown-rump length → redate by ultrasound; the 7-day rule applies before 14 0/7 weeks.
2. Third-trimester ultrasound "measuring small" → evaluate for growth restriction; do not redate.
3. Rh(D)-negative patient with first-trimester bleeding → anti-D immune globulin now, in addition to the routine 28-week dose.
4. "She had Tdap two years ago" → Tdap is repeated in every pregnancy at 27–36 weeks.
5. Non-immune rubella on first-visit labs → vaccinate postpartum, not during pregnancy.
6. Asymptomatic bacteriuria on prenatal urine culture → treat; this is one of the few settings where asymptomatic bacteriuria is treated.
7. Nulliparous 37-year-old with obesity, at 13 weeks → two moderate-risk factors qualify her for low-dose aspirin now.