Severe FGR in the Second Trimester — MFM Clinical Education
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Clinical Review
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Maternal-Fetal Medicine

Severe Fetal Growth Restriction
in the Second Trimester

Diagnosis  ·  Prognosis  ·  Surveillance

SMFM Guideline-Consistent 18–21 Weeks Severe Phenotype
Atlanta Perinatal Associates MFM Education Series
Definition
Early-Onset FGR: A Severe Phenotype
Clinical threshold and occurrence rates before viability.
< 10th
EFW or AC percentile
before 32 weeks
0.5–1%
Prevalence of
early-onset FGR
18–21wk
Highest pretest probability
of intrinsic fetal defects
At 18–21 weeks, intrinsic fetal causes (aneuploidy, structural anomaly, infection) outweigh isolated placental insufficiency.
Atlanta Perinatal Associates MFM Education Series
Etiology
Primary Causes at 18–21 Weeks
Determining the underlying driver is key to mapping clinical course.
🧬
Chromosomal
Trisomy 13, 18, 21
Triploidy
🫀
Structural
Congenital heart disease
Gastroschisis
🦠
Infectious
CMV · Toxoplasmosis
Syphilis · Rubella
🩸
Placental
Severe insufficiency
Maternal hypertension
Pregestational diabetes
Atlanta Perinatal Associates MFM Education Series
Evaluation
Comprehensive Diagnostic Workup
Recommended sequential assessments to map risk and rule out etiologies.
Detailed Anatomical Survey
Comprehensive ultrasound — structural malformations and aneuploidy markers
Genetic Testing
Amniocentesis with chromosomal microarray; UA Doppler often abnormal with aneuploidy
Infectious Disease Screening
Maternal TORCH serology; amniotic fluid PCR if echogenic bowel or calcifications present
Doppler Ultrasonography
Umbilical artery (UA) and uterine artery (UtA) — assess placental vascular perfusion
Maternal Comorbidity Evaluation
Chronic hypertension, pregestational diabetes, antiphospholipid syndrome — present in >80% of maternal-driven cases
Atlanta Perinatal Associates MFM Education Series
Prognosis
A Guarded Prognosis
Balancing expectations and severity benchmarks in extreme early FGR.

Outcome Risks

  • Stillbirth and neonatal death
  • Indicated extreme preterm birth
  • High NICU admission rate
  • High mortality if delivery < 34 weeks

Prognostic Predictors

  • EFW z-score
  • Gestational age at diagnosis
  • Umbilical artery Doppler category
  • AREDV = impending decompensation
Absent or reversed end-diastolic velocity (AREDV) in the umbilical artery signifies impending fetal decompensation and right heart strain.
Atlanta Perinatal Associates MFM Education Series
Management
Surveillance Strategy
Evidence-based recommendations for monitoring early severe FGR.

Not Recommended

  • Heparin / LMWH
  • Sildenafil
  • Dietary modifications
  • Bed rest

Recommended Protocol

  • Serial biometry every 2–4 weeks
  • Weekly UA Doppler once viable
  • Ductus venosus (DV) Doppler
  • Computerized CTG (cCTG)
Delaying delivery until DV pulsatility index or cCTG short-term variation is abnormal improves long-term neurological outcomes (< 32 weeks).
Atlanta Perinatal Associates MFM Education Series
Doppler Surveillance
Escalating Doppler Hierarchy
Hemodynamic transition steps in worsening placental resistance.
1
Umbilical Artery (UA) — Baseline placental resistance
Elevated PI → absent → reversed end-diastolic velocity (AREDV)
2
Middle Cerebral Artery (MCA) — Brain-sparing response
Reduced PI indicates redistribution; used more in late FGR
3
Ductus Venosus (DV) — Cardiac preload marker
Elevated PI or absent/reversed A-wave → venous compromise
4
Computerized CTG (cCTG) — Short-term variation (STV)
STV < 3 ms = critical threshold; guides delivery timing
Atlanta Perinatal Associates MFM Education Series
Clinical Distinction
Early vs. Late-Onset FGR
Key differentiators between early and late phenotypes.
Characteristic Early-Onset FGR (< 32 wk) Late-Onset FGR (≥ 32 wk)
Prevalence 0.5%–1% 5%–10%
Primary Etiology Placental insufficiency, aneuploidy, infection Milder placental dysfunction
Umbilical Artery Doppler Typically abnormal (AREDV common) Typically normal
Maternal Hypertensive Risk High — up to 70% of cases Lower association
Monitoring Focus DV Doppler · cCTG · Prematurity balance MCA Doppler · Cerebroplacental ratio (CPR)
Atlanta Perinatal Associates MFM Education Series
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