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Pregnancy
Fetal growth restriction
Fetal growth restriction (FGR) = estimated fetal weight (EFW) or abdominal circumference (AC) <10th percentile for gestational age. Complicates 5–10% of pregnancies and is a leading cause of perinatal morbidity and mortality.
Board pearl: A small-for-gestational-age (SGA) fetus is a statistical definition (<10th percentile); FGR implies pathology. Not all SGA fetuses are growth-restricted, and some growth-restricted fetuses may be >10th percentile if their genetic potential was higher.
Next best step: Confirm GA → obtain formal ultrasound with EFW, AC, and umbilical artery (UA) Doppler.
— Lagging fundal height (≥3 cm discrepancy from GA between 20–36 wks)
— Inadequate interval growth on serial ultrasounds
— ↓ Amniotic fluid (oligohydramnios) noted on US
— Chronic hypertension or preeclampsia (most common placental cause)
— Tobacco use — dose-dependent ↓ in birth weight (~200 g reduction)
— Cocaine use → vasoconstriction → uteroplacental insufficiency
— Prior pregnancy with FGR or stillbirth
— Antiphospholipid syndrome, SLE, renal disease, diabetes with vasculopathy
— Teratogen exposure (anticonvulsants, warfarin)
— Poor nutritional intake, low prepregnancy BMI
— Assisted reproductive technology (↑ risk even singletons)
Key distinction: Early-onset FGR (<32 wks) is more commonly associated with placental insufficiency and carries higher perinatal morbidity, while late-onset FGR (≥32 wks) is more prevalent but often less severe.
Board pearl: Symmetric FGR presenting in early pregnancy → think chromosomal abnormality or congenital infection rather than placental insufficiency.
Classification of FGR:
— All biometric parameters (head, abdomen, femur) proportionally small
— Onset in first trimester
— Causes: chromosomal abnormalities (trisomy 13, 18, triploidy), congenital infections (CMV, rubella, toxoplasmosis), teratogens
— Prognosis generally worse
— Head circumference (HC) spared relative to AC ("head-sparing" effect due to preferential shunting of blood to the brain)
— Onset in late second/third trimester
— Causes: uteroplacental insufficiency (preeclampsia, chronic HTN, smoking)
— Brain-sparing reflex → ↓ AC due to depleted hepatic glycogen and ↓ subcutaneous fat
Board pearl: Asymmetric FGR with ↓ AC but preserved HC = placental insufficiency → monitor with UA Doppler. Symmetric FGR early in pregnancy = aneuploidy/infection workup.
Ultrasound components:
— HC/AC ratio >1 after 36 wks → asymmetric FGR
— Umbilical artery (UA) Doppler — first-line surveillance tool
— Measures downstream placental resistance
— Normal: forward diastolic flow; abnormal: ↑ S/D ratio → absent end-diastolic flow (AEDF) → reversed end-diastolic flow (REDF)
— REDF = severe placental insufficiency, high risk of fetal demise
Next best step: Once FGR confirmed → UA Doppler to stratify severity and guide management.
— Normally high-resistance vessel
— In FGR with brain-sparing → MCA resistance ↓ (↑ diastolic flow) → low MCA pulsatility index (PI)
— Cerebro-placental ratio (CPR) = MCA PI / UA PI → CPR <1.0 is abnormal → indicates redistribution of blood flow to brain
— Reflects cardiac function and venous return
— Abnormal: absent or reversed a-wave → imminent fetal compromise, ↑ risk of stillbirth within days
— Most important Doppler for timing delivery in early-onset severe FGR
— Detailed anatomy scan for structural anomalies
— Genetic counseling and amniocentesis/microarray (especially symmetric FGR or anomalies)
— TORCH titers (CMV IgM/IgG, toxoplasmosis, rubella) — especially if symmetric + intracranial calcifications, hydrops, hepatosplenomegaly
— Maternal labs: CBC, UA, preeclampsia labs, antiphospholipid antibodies if indicated
— Uterine artery Doppler: bilateral notching → ↑ risk of preeclampsia/FGR
Board pearl: CMV is the most common congenital infection causing FGR — look for periventricular calcifications, ventriculomegaly, and echogenic bowel on US.
Management depends on GA, severity (EFW percentile), and Doppler findings:
— Serial growth US every 2–4 weeks
— Weekly or twice-weekly NST/BPP starting at 32–34 wks
— Delivery by 37–38 weeks if stable
— Serial growth US every 2 weeks
— Twice-weekly NST/BPP
— UA and MCA Doppler weekly
— Delivery by 37 weeks
— Frequent Doppler surveillance (1–3× per week depending on findings)
— Antenatal corticosteroids (betamethasone) if <34 wks
— MgSO₄ for neuroprotection if delivery anticipated <32 wks
— Delivery timing guided by Doppler progression (see next chunk)
Board pearl: There is no treatment that reverses FGR — management focuses on surveillance to optimize delivery timing, balancing risks of prematurity vs. intrauterine demise.
Next best step: Risk-stratify using UA Doppler → this determines surveillance intensity and delivery timing.
Delivery timing is the most critical management decision in FGR:
— If ≥34 wks → deliver after betamethasone
— If <34 wks → hospitalize, daily Doppler/BPP, give betamethasone → deliver at 34 wks or sooner if DV abnormal
— If ≥32 wks → deliver after steroids (give and deliver within 48h)
— If <32 wks → give betamethasone + MgSO₄ → deliver at 32 wks or sooner if DV a-wave absent/reversed
Key distinction: DV abnormality is the final Doppler to become abnormal in the progression of FGR and indicates imminent cardiac decompensation → most predictive of stillbirth.
Board pearl: Delivery method — cesarean is often recommended for AEDF/REDF because these fetuses tolerate labor poorly; however, vaginal delivery is not contraindicated with normal Dopplers and reassuring fetal status.
Adjunctive measures:
— Bed rest — no proven benefit, ↑ risk of VTE
— Maternal oxygen therapy — no sustained benefit
— Volume expansion — ineffective and may worsen preeclampsia
— Sildenafil — studied but STRIDER trials showed no benefit and possible harm
Board pearl: The only definitive "treatment" for FGR is delivery — all management is centered on surveillance to determine optimal timing of delivery.
Management priorities:
Delivery:
Board pearl: In early-onset severe FGR at the limit of viability (22–24 wks), management is individualized with counseling regarding neonatal outcomes — expectant management vs. comfort care vs. delivery.
Key distinction: Early-onset FGR carries 5–10× higher perinatal mortality than late-onset FGR.
Late-onset FGR (≥32 wks):
Multiple gestations:
— UA Doppler findings in donor twin: AEDF/REDF may be intermittent
— MCA Doppler: assess for TAPS (twin anemia-polycythemia sequence)
— May require laser ablation or selective reduction in severe cases
Board pearl: In late-onset FGR with normal UA Doppler, an abnormal CPR (<1.0) is the best predictor of adverse outcome and should prompt ↑ surveillance and earlier delivery consideration.
— EFW <3rd percentile: 1.5% risk of stillbirth
— AEDF: ~4× ↑ stillbirth risk
— REDF: ~10× ↑ stillbirth risk
— Abnormal DV: imminent demise if not delivered
— ↓ Placental reserve → intolerance of contractions → late decelerations, fetal acidosis
— Higher cesarean rate
— Hypoglycemia (↓ glycogen stores) — check glucose within 1 hour of birth
— Hypothermia (↓ subcutaneous fat)
— Polycythemia → hyperviscosity (chronic hypoxia → ↑ erythropoietin)
— Hypocalcemia, hyperbilirubinemia
— Necrotizing enterocolitis (NEC) — due to chronic intestinal hypoperfusion
— Meconium aspiration syndrome (MAS)
— Impaired immune function → ↑ infection risk
— Barker hypothesis: fetal programming → ↑ risk of adult cardiovascular disease, type 2 diabetes, metabolic syndrome
— Neurodevelopmental delays — particularly with early-onset FGR and prematurity
Board pearl: Neonatal hypoglycemia is the most immediate postnatal concern — initiate early feeding and glucose monitoring.
— Preeclampsia/HELLP → seizures, hepatic rupture, DIC
— Antiphospholipid syndrome → thrombosis, recurrent pregnancy loss
— Chronic HTN → stroke, cardiac complications
— Placental abruption (↑ risk in FGR pregnancies) → hemorrhage, DIC
When to escalate care:
— GA <32 wks with severe FGR (need Level III/IV NICU)
— AEDF or REDF on UA Doppler
— Abnormal DV Doppler
— BPP ≤4/10
— Persistent BPP ≤4/10 at viable GA
— Reversed DV a-wave
— Recurrent unprovoked late decelerations
— Terminal fetal heart rate pattern (sinusoidal or recurrent severe variable decels)
— Concurrent maternal deterioration (severe preeclampsia, HELLP, abruption)
Board pearl: The decision to deliver a severely growth-restricted preterm fetus requires balancing the risk of fetal demise in utero against the morbidity and mortality of extreme prematurity — this is best managed at a tertiary care center with MFM and NICU.
— Small parents (especially maternal size), ethnicity-related growth patterns
— Symmetric but all growth parameters track consistently on a low percentile
— Normal UA Doppler, normal amniotic fluid, normal fetal movement
— Customized growth charts (adjusting for maternal height, weight, ethnicity, parity) can help distinguish
— No intervention needed
— Statistical definition: EFW or birth weight <10th percentile
— Includes both pathologic FGR and constitutionally small fetuses
— ~50–70% of SGA fetuses are constitutionally small (not growth-restricted)
— Pathologic process → fetus not reaching genetic growth potential
— Abnormal Doppler, oligohydramnios, or falling growth trajectory across percentiles
— Requires surveillance and delivery timing decisions
Key distinction: A fetus that has been tracking at the 8th percentile consistently with normal Dopplers and fluid is likely constitutionally small. A fetus that drops from the 40th to the 8th percentile over 4 weeks is growth-restricted regardless of crossing the 10th percentile threshold.
Board pearl: Growth velocity (trajectory) is as important as a single EFW measurement — a fetus crossing percentiles downward is concerning even if still above the 10th percentile.
— Trisomy 18: severe symmetric FGR + clenched fists, choroid plexus cysts, cardiac defects
— Trisomy 13: symmetric FGR + holoprosencephaly, cleft lip
— Triploidy: severe early-onset FGR + partial molar placenta
— Turner syndrome (45,X): mild FGR + cystic hygroma, hydrops
— CMV: most common infectious cause → periventricular calcifications, echogenic bowel, hepatosplenomegaly
— Toxoplasmosis: diffuse intracranial calcifications, hydrocephalus
— Rubella: cataracts, cardiac defects, deafness
— Syphilis: hydrops, hepatosplenomegaly, osteitis
Board pearl: If FGR is symmetric and early-onset with structural anomalies → amniocentesis for karyotype/microarray is the next best step, not just Doppler surveillance.
— Uterine artery Doppler at 20–24 wks: bilateral notching or ↑ PI → ↑ risk of FGR/preeclampsia
— Serial growth US every 3–4 wks starting at 24–28 wks if risk factors present
— PAPP-A <5th percentile or ↑ AFP on first/second-trimester screening → ↑ FGR risk → enhanced surveillance
— Low-dose aspirin (81 mg daily) starting at 12–16 wks in patients at high risk for preeclampsia → reduces FGR risk by ~20%
— Smoking cessation counseling — most impactful modifiable intervention
— Cocaine/substance abuse treatment
— Optimal management of chronic conditions (HTN, diabetes, SLE, APS)
— Nutritional counseling and appropriate weight gain
— Anticoagulation (LMWH) for antiphospholipid syndrome
Board pearl: Low-dose aspirin is the only pharmacologic intervention with proven efficacy in PREVENTING FGR in high-risk populations — it must be started before 16 weeks to be effective.
— Serial growth US: every 2–4 wks (more frequent with abnormal Dopplers)
— Fetal surveillance: NST and/or BPP weekly to biweekly
— Doppler reassessment: UA → MCA → DV (escalating based on severity)
— Daily fetal kick counts starting at 28 wks
— Continuous electronic fetal monitoring (EFM) — FGR fetuses have ↓ reserve
— Low threshold for cesarean if non-reassuring tracing
— Avoid oxytocin overstimulation (tachysystole worsens an already compromised fetus)
— Amnioinfusion if recurrent variable decelerations
— Neonatal evaluation: weight, head circumference, Ponderal index
— Immediate glucose check and temperature monitoring
— Placental pathology: send for histology — may reveal infarcts, vasculopathy, or infection → guides future pregnancy counseling
— Maternal debrief and recurrence counseling (recurrence risk ~20%)
— Screen for underlying causes not previously identified (thrombophilia, renal disease)
Board pearl: Always send the placenta for pathologic examination after FGR delivery — findings (e.g., villous infarction, decidual vasculopathy, chronic villitis) help predict recurrence and guide management in subsequent pregnancies.
— Severe early-onset FGR may require delivery at the limit of viability
— Shared decision-making is essential — discuss realistic neonatal outcomes, survival rates, and long-term disability
— Options: active intervention (steroids, MgSO₄, cesarean, NICU) vs. comfort care
— Parental values and goals of care must guide decisions
— If mother declines recommended delivery despite non-reassuring fetal status → document counseling thoroughly; court-ordered interventions are ethically controversial and generally discouraged
— Encourage open dialogue; involve ethics committee if needed
— Failure to obtain growth US when fundal height is lagging → common malpractice claim
— Failure to initiate Doppler surveillance after FGR diagnosis
— Failure to deliver in timely fashion once non-reassuring testing occurs
Board pearl: On boards, the ethical principle tested is usually informed consent and shared decision-making — the physician should present all options with risks/benefits but not override patient autonomy.
Board pearl: The Doppler cascade in FGR follows a predictable sequence — UA abnormality first, then MCA brain-sparing, then DV abnormality (reflecting cardiac decompensation) — DV is the final harbinger of fetal demise.
