Fetal Growth Assessment

Growth Fundamentals - Size Matters!

• Fetal growth assessment is vital for detecting deviations, guiding management, and reducing perinatal risks.
• Key Definitions:
  • IUGR (Intrauterine Growth Restriction): Estimated Fetal Weight (EFW) or Abdominal Circumference (AC) < 10th percentile for gestational age (GA). Pathological restriction.
  • SGA (Small for Gestational Age): Birth weight < 10th percentile for GA. Can be constitutional or IUGR.
  • LGA (Large for Gestational Age): Birth weight > 90th percentile for GA.
  • Macrosomia: Absolute birth weight > 4000g (or > 4500g).

⭐ Symmetric vs. Asymmetric IUGR:

• Symmetric IUGR: Early insult (1st/2nd trimester; e.g., aneuploidy, TORCH infections). All fetal parameters proportionally small.
• Asymmetric IUGR: Late insult (3rd trimester; e.g., uteroplacental insufficiency, maternal hypertension). Head spared (brain-sparing effect), AC ↓ significantly more than HC/FL.

Assessment Toolkit - Tapes to Tech

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Doppler Deep Dive - Flowing Forward

• Assesses fetal well-being, placental function; vital in IUGR.
• Key Vessels & Indices:
  • Umbilical Artery (UA):
    • ↑S/D ratio (>3 post 30wks), ↑PI/RI → placental insufficiency.
    • Absent/Reversed End-Diastolic Flow (AEDF/REDF) → severe compromise.
  • Middle Cerebral Artery (MCA):
    • ↓PI → "brain sparing".
    • ↑Peak Systolic Velocity (PSV >1.5 MoM) → fetal anemia.
  • Ductus Venosus (DV):
    • Abnormal a-wave (absent/reversed) → cardiac dysfunction, high risk.
  • Uterine Artery:
    • Persistent ↑PI/notching >24wks → pre-eclampsia/IUGR risk.
• Cerebroplacental Ratio (CPR):
  • $CPR = \frac{MCA \ PI}{UA \ PI}$; Normal >1.
  • ↓CPR (<1) → fetal hypoxia.

⭐ Reversed end-diastolic flow (REDF) in umbilical artery is an ominous sign indicating severe fetal compromise.

Managing Growth Curves - Action Stations

• FGR Confirmed (EFW/AC < 10th %ile):
  • Goal: Optimize outcome, timely delivery.
  • Serial growth scans (2-3 wks).
  • Doppler surveillance (UA, MCA, CPR, DV) frequency varies.
  • Antenatal corticosteroids (ACS) if delivery < 34 wks.
  • MgSO₄ for neuroprotection if delivery < 32 wks.
• Delivery Timing:
  • Late FGR (>32 wks, normal Dopplers): Aim 37-38 wks.
  • Early FGR / abnormal Dopplers: Individualize.

⭐ Key indications for delivery in early FGR: Reversed End-Diastolic Flow (REDF) in Umbilical Artery (UA), or abnormal Ductus Venosus (DV) flow. Delivery often considered from 26-28 weeks if DV abnormal, or 30-32 weeks for UA REDF.

High‑Yield Points - ⚡ Biggest Takeaways

• SFH correlates with GA (20-24 to 34-36 weeks); discrepancies warrant USG.
• USG is gold standard for biometry (BPD, HC, AC, FL) and EFW.
• AC is most sensitive for FGR & macrosomia detection.
• EFW uses Hadlock's formula (BPD, HC, AC, FL).
• UA Doppler is key for FGR management, indicating placental insufficiency.
• Oligohydramnios (AFI < 5 cm) is often linked with FGR.
• SGA is EFW < 10th percentile; FGR implies pathological growth restriction.