What is the recommended spacing of prenatal exams based on gestational age (GA)?

Recommended Prenatal Visit Schedule by Gestational Age

For uncomplicated, low-risk pregnancies, prenatal visits should be scheduled monthly until 28 weeks' gestation, then every 2 weeks until 36 weeks, followed by weekly visits until delivery—a schedule established in 1930 that remains the standard despite lack of original supporting evidence. 1

Standard Visit Schedule for Low-Risk Pregnancies

• Monthly visits from initial presentation through 28 weeks' gestation to monitor maternal health, screen for gestational diabetes (at 24-28 weeks), and assess fetal growth 1

• Biweekly visits from 28 to 36 weeks' gestation to increase surveillance as pregnancy advances and risks of complications rise 1

• Weekly visits from 36 weeks until delivery to monitor for signs of labor, assess fetal well-being, and detect late-developing complications 1

This traditional schedule typically results in 12-14 total visits during pregnancy, depending on when prenatal care begins 1

Key Timing for Specific Assessments

First Trimester (up to 14 weeks)

• Initial visit should occur as early as possible for dating ultrasound (ideally 8-14 weeks using crown-rump length), baseline laboratory testing, and risk assessment 2

• Women with BMI ≥30 kg/m² require early gestational diabetes screening at 12-14 weeks, with repeat testing at 24-28 weeks if initial screen is negative 3

• Women with prior gestational diabetes should undergo glucose testing at the first prenatal visit (typically 12-14 weeks or earlier), then retest at 24-28 weeks if negative 3

Second Trimester (14-28 weeks)

• Anatomy ultrasound scan at 18-20 weeks to evaluate fetal structure and development 4

• Universal gestational diabetes screening at 24-28 weeks for all women not previously diagnosed 3

Third Trimester (28 weeks to delivery)

• Routine 36-week ultrasound can identify non-cephalic presentation, allowing time for external cephalic version or planning for cesarean delivery 5

• Visits increase to weekly after 36 weeks to monitor for onset of labor and assess fetal well-being 1

Modified Schedules for High-Risk Pregnancies

Hypertensive Disorders and Preeclampsia

• At diagnosis of preeclampsia, immediate fetal biometry, amniotic fluid assessment, and Doppler studies are required 1

• Serial ultrasound evaluations every 2 weeks minimum for fetal growth, amniotic fluid, and umbilical artery Doppler from 24 weeks until birth in confirmed preeclampsia 1

• More frequent ultrasound if high umbilical artery resistance or absent/reversed end-diastolic flow is detected, requiring specialized maternal-fetal medicine consultation 1

Fetal Growth Restriction

• Biweekly ultrasound assessments are the minimum interval for evaluating fetal growth once restriction is suspected or confirmed 1, 2

• Weekly or twice-weekly antenatal surveillance (biophysical profile or non-stress testing) becomes standard at 32-34 weeks' gestation for most high-risk conditions, though this frequency lacks rigorous scientific evidence 1

Multiple Gestations

• More frequent monitoring than singleton pregnancies, including first trimester dating, nuchal translucency scan, anatomy scan, and one or more third-trimester growth scans 4

• Monochorionic twin pregnancies require more intensive surveillance due to higher complication rates, with visit frequency determined by specific risks 4

Important Clinical Caveats

Historical Context and Evidence Limitations

The current prenatal visit schedule was recommended in 1930 by the Children's Bureau without supporting evidence and has remained essentially unchanged through 2017 guidelines despite drastic changes in technology, population health, and evidence supporting alternative delivery models 1

This one-size-fits-all approach has persisted despite the United States having persistently worse maternity outcomes and deepening health disparities compared to other developed nations 1

Antenatal Testing Limitations

• No single antenatal test has proven superior for identifying fetuses at risk of intrauterine demise 1

• A normal test result is highly reassuring, with false negatives (stillbirth within 1 week of normal test) being uncommon regardless of test used 1

• Antenatal surveillance cannot predict stillbirth from acute events such as placental abruption or cord accidents 1

• Routine antenatal testing does not improve outcomes in low-risk pregnancies and may cause iatrogenic prematurity from false-positive results 1

Common Pitfalls to Avoid

• Failing to screen high-risk women early in pregnancy (particularly those with BMI ≥30 kg/m² or prior gestational diabetes) results in delayed intervention and increased complications 3

• Not repeating gestational diabetes screening at 24-28 weeks in high-risk women who initially test negative leads to delayed diagnosis and treatment 3

• Missing the 18-20 week anatomy scan or delaying it in obese patients without appropriate follow-up at 20-22 weeks can result in missed anomalies 4

• Overlooking the need for additional ultrasound assessment when patients present in labor, even if a 36-week scan showed cephalic presentation, since 0.3% spontaneously rotate to non-cephalic presentation after that scan 5