Fetal growth below the 10th percentile for gestational age due to a pathologic process.
Also known as: IUGR, FGR, fetal growth restriction, small for gestational age, SGA
Overview
Fetal growth restriction (now the preferred term, FGR) is defined by ACOG/SMFM as estimated fetal weight or abdominal circumference below the 10th percentile for gestational age. SGA refers to a constitutionally small but otherwise healthy fetus; IUGR/FGR implies a pathologic process limiting growth.
Epidemiology
Affects 3-10% of pregnancies. Strongly associated with stillbirth, perinatal morbidity, and long-term cardiometabolic and neurodevelopmental disease (Barker hypothesis).
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Symmetric IUGR (proportional reduction of head and body) typically reflects an early-pregnancy insult — chromosomal abnormality or infection. Asymmetric IUGR (head sparing, with disproportionately small abdomen) reflects later-pregnancy uteroplacental insufficiency, with preferential blood flow to brain at the expense of the liver and subcutaneous tissue.
Clinical presentation
Symptoms
Often asymptomatic; detected on screening
Decreased fetal movement may indicate fetal compromise
Signs / physical exam
Fundal height lagging >=3 cm behind gestational age
Low maternal weight gain
Findings of associated maternal disease (e.g., hypertension)
Differential diagnosis
Constitutionally small (SGA) — Normal growth velocity on serial scans, normal Doppler studies, no risk factors; family history of small but healthy infants
Inaccurate dating — LMP unreliable; recheck with first-trimester crown-rump length (most accurate)
Oligohydramnios alone — Low AFI without growth lag — consider PROM, urinary tract anomaly
Diagnostic workup
Diagnostic criteria
Delphi consensus: EFW or AC <3rd percentile alone, OR EFW <10th percentile combined with abnormal Doppler indices or low growth velocity.
Labs
Targeted maternal evaluation: CMP, urine protein/creatinine ratio (preeclampsia), antiphospholipid antibodies if recurrent
TORCH serologies if early-onset, symmetric, or with anomalies
Umbilical artery Doppler velocimetry — cornerstone of surveillance in FGR; assess for increased resistance, absent end-diastolic flow (AEDF), or reversed end-diastolic flow (REDF)
Middle cerebral artery (MCA) Doppler and ductus venosus Doppler in advanced or early-onset disease
Detailed anatomy scan to evaluate for structural anomalies
Diagnostic algorithm
Pattern
Timing of Insult
Typical Etiology
Head:Abdomen Ratio
Symmetric
Early (1st-early 2nd trimester)
Aneuploidy, TORCH infection, teratogen
Normal (proportional)
Asymmetric
Late (late 2nd-3rd trimester)
Placental insufficiency, maternal HTN/PEC
Increased (head sparing)
Symmetric vs asymmetric IUGR patterns.
Treatment
First-line
Identify and treat reversible causes (smoking cessation, BP control, anticoagulation for APS)
Antepartum surveillance: weekly to twice-weekly NSTs and/or BPPs, growth ultrasound every 2-4 weeks, serial umbilical artery Dopplers
Antenatal corticosteroids if delivery anticipated 24 0/7 to 33 6/7 wk (consider 34 0/7 to 36 6/7 wk per ACOG)
Magnesium sulfate for neuroprotection if delivery <32 wk
Delivery timing (SMFM/ACOG)
Isolated FGR with normal Dopplers: 36 0/7 to 37 6/7 wk
FGR with comorbid condition or oligohydramnios: 34 0/7 to 37 6/7 wk
FGR with absent end-diastolic flow: 34 0/7 wk
FGR with reversed end-diastolic flow: 30 0/7 wk
Any FGR with abnormal BPP or fetal compromise: deliver
Second-line / adjunct
Low-dose aspirin (81 mg daily, started ideally <16 wk) for women at high risk of preeclampsia/placental insufficiency
Mode of delivery individualized — cesarean preferred for REDF or non-reassuring monitoring; vaginal delivery acceptable in many cases with continuous monitoring
Complications
Stillbirth (risk increases with severity and abnormal Dopplers)
Absent or reversed end-diastolic flow on umbilical artery Doppler are markers of severe placental insufficiency requiring escalation of care and consideration of delivery.
Symmetric IUGR raises concern for early insult — order TORCH and consider aneuploidy testing.
Always re-verify dating before diagnosing IUGR — first-trimester ultrasound is the gold standard.
Aspirin 81 mg from 12-16 wk reduces preeclampsia and may reduce FGR in high-risk patients (USPSTF Grade A).
FGR is not the same as SGA — about 70% of fetuses with EFW <10th percentile are constitutionally small and healthy.
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