When should fetal growth restriction be suspected in a pregnant patient based on gestational age, ultrasound biometry, fundal‑height lag, oligohydramnios, maternal risk factors (e.g., chronic hypertension, pre‑eclampsia, diabetes, smoking, substance abuse, prior FGR, uterine anomalies, antiphospholipid syndrome) or abnormal Doppler studies?

When to Consider Fetal Growth Restriction

Fetal growth restriction (FGR) should be suspected when ultrasound shows an estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for gestational age, or when fundal height measurements lag by more than 3 cm below gestational age in weeks, prompting immediate ultrasound evaluation with Doppler studies. 1

Primary Screening Triggers

Fundal Height Discrepancies

• Fundal height >3 cm less than gestational age (McDonald rule) requires immediate ultrasound evaluation 1, 2
• Fundal height <10th percentile on customized growth charts necessitates ultrasound 1
• Slow or static growth with <5 mm change over 14 days warrants ultrasound assessment 1, 2
• Serial fundal height measurement should begin at 24-26 weeks and continue at every prenatal visit 1

Important caveat: Fundal height is unreliable in obesity, multiple gestations, fibroids, polyhydramnios, or non-longitudinal fetal lie—proceed directly to ultrasound in these situations 2

Ultrasound Biometry Thresholds

• EFW or AC <10th percentile is the standard definition of FGR 1
• EFW <3rd percentile indicates severe FGR requiring intensified surveillance regardless of Doppler findings 1
• Population-based references (such as Hadlock curves) should be used rather than customized standards 1

Maternal Risk Factors Requiring Enhanced Surveillance

High-Risk Conditions Warranting Early Screening

• Chronic hypertension or preeclampsia—present in 50-70% of early-onset FGR cases and independently predicts poor outcomes 1
• Prior FGR pregnancy—consider low-dose aspirin <16 weeks for prevention 1
• Antiphospholipid syndrome—associated with placental insufficiency 1
• Diabetes with vascular complications—increases placental dysfunction risk 1
• Smoking or substance abuse—modifiable risk factors requiring cessation counseling 1
• Uterine anomalies—may compromise placental perfusion 1

These risk factors should trigger umbilical artery Doppler assessment starting at 26-28 weeks gestation 1

Associated Findings That Strengthen Suspicion

Oligohydramnios

• Amniotic fluid index (AFI) <5 cm or maximum vertical pocket (MVP) <2 cm reflects chronic placental insufficiency with decreased fetal renal perfusion 1, 3
• Severe oligohydramnios (AFI <3 cm) is an independent indication for delivery consideration at term 3
• Oligohydramnios combined with FGR significantly increases perinatal risk and argues against expectant management 3

Abnormal Doppler Studies

• Umbilical artery pulsatility index >95th percentile (decreased end-diastolic velocity) indicates placental vascular resistance and confirms pathological FGR 1
• Absent end-diastolic velocity (AEDV) requires 2-3 times weekly Doppler assessment due to rapid deterioration risk 1
• Reversed end-diastolic velocity (REDV) mandates hospitalization, corticosteroids, and delivery consideration regardless of gestational age 1
• **Middle cerebral artery pulsatility index <5th percentile** (brain-sparing) suggests fetal hypoxemia, particularly in late-onset FGR >32 weeks 4, 5

The presence of abnormal umbilical artery Doppler combined with EFW <10th percentile is widely accepted as definitive evidence of pathological FGR rather than constitutional smallness 4, 5

Gestational Age-Specific Considerations

Early-Onset FGR (<32 weeks)

• Up to 20% have associated fetal malformations or chromosomal abnormalities—detailed anatomic survey (CPT 76811) is mandatory 1
• Chromosomal microarray analysis should be offered for unexplained isolated FGR <32 weeks 1
• PCR testing for cytomegalovirus (CMV) is recommended if amniocentesis is performed; routine screening for toxoplasmosis, rubella, or herpes is not indicated 1
• Umbilical artery Doppler abnormalities are the hallmark finding 6, 7

Late-Onset FGR (≥32 weeks)

• Often presents with subtle Doppler changes and normal umbilical artery studies 6, 7
• Middle cerebral artery Doppler and cerebroplacental ratio become more relevant for risk stratification 4, 5
• Frequently unrecognized but contributes substantially to adverse perinatal outcomes at term 7

Clinical Presentation Patterns

Decreased Fetal Movement

• Warrants comprehensive ultrasound with biometry, amniotic fluid assessment, and umbilical artery Doppler to exclude chronic placental insufficiency 8
• May be the presenting symptom of previously undiagnosed FGR 8

Fetal Malformations or Polyhydramnios

• When detected alongside small fetal size, diagnostic testing including chromosomal microarray should be offered regardless of gestational age 1

Common Pitfalls to Avoid

Do not rely on fundal height alone in high-risk patients—proceed directly to ultrasound biometry and Doppler assessment 2

Do not assume all small fetuses are pathological—18-22% of fetuses <10th percentile are constitutionally small with normal outcomes 1, 9

Do not delay Doppler assessment once FGR is suspected—umbilical artery Doppler is essential to differentiate pathological FGR from constitutional smallness and guide surveillance intensity 1, 9

Do not use customized growth standards—population-based references (Hadlock) are recommended over customized charts 1