In a 32‑week pregnant patient with symphysis‑fundal height 2 weeks below expected, abdominal circumference at the 5th percentile, amniotic fluid deepest vertical pocket 2 cm, and cerebro‑placental ratio at the 5th percentile, which diagnosis is most likely: normal growth, small‑for‑gestational‑age, early‑onset fetal growth restriction, or late‑onset fetal growth restriction?

Late-Onset Fetal Growth Restriction

This is late-onset fetal growth restriction (FGR), not simply small-for-gestational-age, based on the combination of AC at the 5th percentile with cerebroplacental ratio at the 5th percentile at 32 weeks gestation.

Diagnostic Rationale

The diagnosis hinges on applying the expert consensus definition for late-onset FGR (≥32 weeks):

• AC at 5th percentile meets the contributory parameter of AC <10th percentile 1
• CPR at 5th percentile is a key contributory parameter that distinguishes true FGR from constitutional SGA, indicating placental insufficiency with brain-sparing physiology 1
• The combination of two contributory parameters establishes the diagnosis of late-onset FGR per international consensus criteria 1

Why Not the Other Options?

Not normal growth (option a): The AC at 5th percentile with abnormal CPR indicates pathologic smallness, not normal variation 1.

Not simple SGA (option b): SGA refers to fetuses <10th percentile without evidence of placental dysfunction who have near-normal perinatal outcomes 2, 3, 4. The CPR at 5th percentile demonstrates placental insufficiency and brain-sparing redistribution, elevating this beyond constitutional smallness 1, 5.

Not early-onset FGR (option c): By definition, early-onset FGR is diagnosed <32 weeks gestation 1. This case presents exactly at 32 weeks, which is the threshold for late-onset classification 1.

Clinical Significance of the 32-Week Threshold

The 32-week cutoff is not arbitrary—it represents distinct pathophysiology:

• Early-onset FGR (<32 weeks) typically shows severe placental dysfunction with progression to abnormal umbilical artery and venous Doppler, strong association with maternal hypertensive disorders, and more extensive placental histopathology 1, 6
• Late-onset FGR (≥32 weeks) represents 70-80% of FGR cases, is typically milder, shows different cardiovascular adaptation patterns with cerebral Doppler abnormalities predominating, and has less extensive placental underperfusion 1, 6, 5

Critical Management Implications

Immediate surveillance protocol:

• Umbilical artery Doppler every 1-2 weeks initially to assess stability, then every 2-4 weeks if stable 1
• Weekly cardiotocography for fetal well-being assessment 1
• Consider repeat biometry every 2 weeks to monitor growth velocity 1
• MCA Doppler and CPR monitoring every 2 weeks given the already abnormal CPR 1

Delivery timing with normal umbilical artery Doppler:

• Delivery at 37-38 weeks is recommended for late-onset FGR with abnormal CPR but normal umbilical artery Doppler 1
• If umbilical artery Doppler becomes abnormal (>95th percentile), deliver by 37-38 weeks 1

Common Pitfalls to Avoid

Do not rely solely on umbilical artery Doppler to differentiate FGR from SGA—umbilical artery Doppler identifies only severe early-onset placental insufficiency 2, 3, 4. The CPR is more sensitive for late-onset FGR 1, 5.

Do not dismiss the deepest vertical pocket of 2 cm as reassuring—while technically normal (>2 cm), this is at the lower threshold and warrants continued amniotic fluid monitoring 1.

Do not delay delivery beyond 38 weeks with abnormal CPR, as late-onset FGR with Doppler evidence of placental insufficiency carries increased risk of stillbirth and suboptimal neurodevelopment 5.