Fetal Microcephaly Diagnostic Workflow

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] HC measurement + distinguish FGR + cause
   HC measurement + distinguish from FGR + brain structure/cause? (Microcephaly = HC <2 SD (severe <3 SD, for gestation and sex). Must distinguish from FGR (HC/AC, whether symmetrically small, serial measurement). Microcephaly often only apparent in the third trimester (serial HC). Sloping forehead. Check sulcation (simplified vs lissencephaly), calcification, associated anomalies.)
   • HC <2–3 SD, normal brain structure and sulcation, proportionate body (suspect FGR/constitutional) → Suspect FGR / constitutional
   • Borderline HC, isolated, familial → Borderline/isolated · serial monitoring
   • HC <3 SD + simplified sulcation/cortical abnormality or associated anomalies/calcification → Severe + brain abnormality · poor prognosis
2. [End] Suspect FGR / constitutional
   Suspect FGR or constitutional microcephaly (HC/AC suggests symmetric smallness, small maternal family head size): serial biometry + umbilical/MCA Doppler to distinguish FGR; if FGR, monitor as FGR; if constitutional, correlate with parental head circumference; still exclude infection and genetics.
3. [End] Borderline/isolated · serial monitoring
   Borderline/isolated microcephaly: serial HC monitoring for progression + detailed brain structure (fetal MRI for sulcation/CC) + infection screen (CMV/Zika) + karyotype/microarray; isolated mild has a generally better outcome but needs postnatal confirmation.
4. [End] Severe + brain abnormality · poor prognosis
   Severe microcephaly (<3 SD) + simplified sulcation/cortical abnormality/associated anomalies/calcification: high neurodevelopmental impairment risk; fetal MRI to assess sulcation (simplified vs lissencephaly)/migration/calcification + infection screen (CMV/Zika) + chromosomal microarray + exome (combined yield ~50%; MCPH/WDR62/ASPM) + genetic counselling.

Source guidelines & references

• Fetal microcephaly evaluation (HC <2/3 SD; simplified sulcation; UOG 2024)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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