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).
Try two board-style Intrauterine Growth Restriction questions
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Question 1ReproductiveMedium
A 29-year-old woman at 33 weeks of gestation with chronic hypertension presents for a routine visit. Her fundal height measures 28 cm, 5 cm behind that expected for dates confirmed by a first-trimester crown-rump length. Maternal weight gain has been minimal. Ultrasound shows an estimated fetal weight at the 5th percentile with a disproportionately small abdominal circumference relative to the head, an amniotic fluid index of 4 cm, and an umbilical artery Doppler with elevated systolic-to-diastolic ratio. Serial scans confirm a declining growth velocity. Which of the following is the most likely diagnosis?
AConstitutionally small fetus, SGA
BPreterm prelabor membrane rupture
CFetal growth restriction (FGR)
DFetal urinary tract obstruction
Reveal answer & full explanation
Correct answer: C — Fetal growth restriction (FGR)
AConstitutionally small fetus, SGA
BPreterm prelabor membrane rupture
CFetal growth restriction (FGR)✓
DFetal urinary tract obstruction
Why Fetal growth restriction (FGR) is correct
An estimated fetal weight below the 10th percentile (here the 5th) combined with abnormal umbilical artery Doppler and declining growth velocity meets the Delphi/ACOG-SMFM criteria for FGR, a pathologic process rather than a constitutionally small fetus.
The asymmetric pattern (head sparing with a disproportionately small abdomen), low amniotic fluid, a maternal risk factor (chronic hypertension), and elevated Doppler resistance all point to uteroplacental insufficiency.
Fundal height lagging >=3 cm behind an accurately dated gestation is the classic screening trigger for FGR.
Why the others are wrong
Constitutionally small fetus, SGA — a small but healthy fetus shows normal growth velocity on serial scans and normal Doppler studies with no risk factors; this fetus has abnormal Dopplers and falling velocity.
Preterm prelabor membrane rupture — ruptured membranes lower the amniotic fluid index but do not restrict growth, and rupture would not produce an estimated fetal weight at the 5th percentile with a disproportionately small abdominal circumference and elevated umbilical artery resistance.
Fetal urinary tract obstruction — obstructive uropathy reduces fetal urine output and can cause oligohydramnios, but it produces a distended bladder or hydronephrosis on ultrasound rather than a head-sparing growth lag with abnormal Doppler, and it does not explain the declining growth velocity in a mother with chronic hypertension.
Question 2ReproductiveMedium
A 29-year-old woman at 30 weeks' gestation, G2P1, is seen for routine prenatal care. Her pregnancy is complicated by chronic hypertension managed with labetalol. Fundal height measures 26 cm, lagging behind prior visits. Dating was confirmed by first-trimester crown-rump length. Ultrasound biometry shows an estimated fetal weight at the 6th percentile with a disproportionately small abdominal circumference; the amniotic fluid index is normal. Which of the following is the most appropriate next diagnostic test?
AMaternal serum TORCH antibody panel
BUmbilical artery Doppler imaging
CAmniocentesis for fetal karyotyping
DRepeat growth ultrasound in 4 weeks
Reveal answer & full explanation
Correct answer: B — Umbilical artery Doppler imaging
AMaternal serum TORCH antibody panel
BUmbilical artery Doppler imaging✓
CAmniocentesis for fetal karyotyping
DRepeat growth ultrasound in 4 weeks
Why Umbilical artery Doppler imaging is correct
Once fetal growth restriction (EFW <10th percentile) is identified, umbilical artery Doppler velocimetry is the cornerstone of surveillance and the next study; per ACOG/SMFM it is the only intervention shown to improve outcomes in FGR.
It distinguishes pathologic placental insufficiency from a constitutionally small fetus and stratifies delivery timing: increased resistance, absent end-diastolic flow (deliver ~34 wk), or reversed end-diastolic flow (deliver ~30 wk).
This asymmetric (head-sparing) pattern with maternal chronic hypertension strongly suggests uteroplacental insufficiency, making Doppler assessment essential now.
Why the others are wrong
Maternal serum TORCH antibody panel: appropriate for early-onset, symmetric FGR or when anomalies/infection are suspected; this is late-onset, asymmetric, with a clear placental cause, so TORCH testing is low-yield.
Amniocentesis for fetal karyotyping: aneuploidy testing is reserved for symmetric, early FGR or FGR with structural anomalies; asymmetric growth from placental insufficiency does not warrant invasive testing here.
Repeat growth ultrasound in 4 weeks: growth scans are repeated every 2-4 weeks, but deferring assessment without Doppler in a fetus with confirmed FGR and a hypertensive mother delays detection of fetal compromise.
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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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