Intrauterine Growth Restriction (IUGR)
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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Risk factors
- Maternal: hypertensive disorders (chronic HTN, preeclampsia), pregestational diabetes with vasculopathy, autoimmune (APS, SLE), severe anemia, malnutrition, low pre-pregnancy BMI, cyanotic cardiac disease
- Behavioral: smoking, alcohol, cocaine, opioid use
- Placental: placental insufficiency, abruption, infarction, single umbilical artery, velamentous insertion
- Fetal: aneuploidy (trisomy 13, 18, 21, Turner), congenital malformation, multiple gestation, congenital infection (TORCH — toxoplasmosis, CMV, rubella, syphilis, varicella)
Pathophysiology
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
- Aneuploidy screening / diagnostic testing per indication (cell-free DNA, amniocentesis, microarray)
Imaging
- Ultrasound biometry: biparietal diameter, head circumference, abdominal circumference, femur length — EFW <10th percentile
- Amniotic fluid index or single deepest pocket
- 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) |
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)
- Neonatal hypoxia, meconium aspiration, hypoglycemia, hypothermia, polycythemia, hypocalcemia
- Long-term: neurodevelopmental impairment, hypertension, insulin resistance, cardiovascular disease (DOHaD/Barker hypothesis)
PANCE pearls
- 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.
References
- ACOG PB 227 — ACOG Practice Bulletin 227: Fetal Growth Restriction (Obstet Gynecol 2021)
- SMFM Consult #52 — SMFM Consult Series #52: Diagnosis and Management of FGR (Am J Obstet Gynecol 2020)
- USPSTF 2021 — USPSTF Grade A: Aspirin Use to Prevent Preeclampsia and Related Morbidity and Mortality
- TRUFFLE — Lees et al., Lancet 2015 — Ductus venosus Doppler vs CTG-guided delivery timing in early FGR
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