Maternal/Placental factors: Uteroplacental insufficiency secondary to maternal HTN/preeclampsia, pregestational DM, smoking/substance abuse, APS/SLE, severe malnutrition, placental abruption, post-term pregnancy.
Clinical Features
Lagging Fundal Height: Fundal height measurement ≥ 3 cm smaller than expected for GA (measured from pubic symphysis to uterine fundus at ≥ 20 wks).
Symmetric FGR: Proportionately small fetus (head circumference = abdominal circumference). Early onset.
Asymmetric FGR: Disproportionate growth (“head-sparing”, head circumference > abdominal circumference due to selective blood flow redistribution to brain, myocardium, and adrenal glands). Late onset.
Diagnosis
Initial/Screening: Fundal height measurement during routine prenatal visits.
Confirmatory/Gold Standard: Obstetric Ultrasound (Biometry) demonstrating EFW or AC < 10th percentile.
Absent or Reversed End-Diastolic Flow (ARED flow) indicates severe placental insufficiency and imminent fetal risk.
Etiologic Workup:
Amniocentesis (karyotype/CMA) and TORCH PCR if early-onset, symmetric, or associated with structural anomalies.
Differential Diagnostics
Constitutional Small for Gestational Age (SGA):
Diff: EFW < 10th percentile with normal Doppler studies, normal growth velocity, normal amniotic fluid volume, and healthy small parents. No intrinsic pathology.
Inaccurate Gestational Age (Incorrect LMP):
Diff: Serial US shows appropriate growth velocity along a lower curve; re-dating required if early 1st-trimester US Crown-Rump Length (CRL) discordant with LMP dates.
Isolated Oligohydramnios:
Diff: Amniotic Fluid Index (AFI ≤ 5 cm) reduced with normal EFW biometry.
Management
Antenatal Surveillance:
Serial US biometry q3–4wks to monitor fetal growth velocity.
Serial UA Doppler weekly or biweekly.
Fetal assessment: NST and BPP 1–2x/week.
Timing of Delivery:
Normal UA Doppler: Deliver at 37–38 weeks GA.
Decreased/Elevated S/D ratio: Deliver at 37 weeks GA.
Absent End-Diastolic Flow (AEDF): Deliver at 34 weeks GA.
Reversed End-Diastolic Flow (REDF) or nonreassuring NST/BPP: Deliver at 32 weeks GA (or earlier) via Cesarean delivery.
Antenatal Corticosteroids: Administer (e.g., Betamethasone) if delivery expected < 37 weeks GA.
Prevention: Low-dose aspirin started before 16 weeks GA in patients with high risk for uteroplacental insufficiency (e.g., prior preeclampsia or FGR).