Biparietal diameter at 11 to 13 weeks' gestation in fetuses with holoprosencephaly.

OBJECTIVE

Studies have suggested that fetuses with holoprosencephaly have smaller head size, demonstrated as early as the first trimester. However, the majority of these cases were diagnosed in the second or third trimesters. The aim of this study was to investigate biparietal diameter (BPD) measured at 11 to 13 weeks' gestation in fetuses with holoprosencephaly.

METHODS

This was a retrospective study in which BPD was measured at 11 to 13 weeks in 34 fetuses with prenatal diagnosis of holoprosencephaly and 7775 unaffected controls. BPD values were converted into multiples of the expected median (MoM) after adjustment for crown-rump length and maternal characteristics.

RESULTS

The median gestational age at the BPD recording was 12.6 (interquartile range 12.3-13.0) weeks. The nuchal translucency was increased (≥3mm) in 58.8% of the cases. Aneuploidy was confirmed in 73.5% of the cases; the commonest was trisomy 13 (50.0%). BPD values at 11 to 13 weeks were below the 5(th) centile in 32.4% of cases and below the 50(th) centile in 67.6%. BPD MoM values were significantly smaller than in the control group (median: 0.98; interquartile range: 0.90-1.06 vs 1.00; 0.96-1.04 MoM, p = 0.03).

CONCLUSION

Fetuses with holoprosencephaly have a smaller BPD in the first trimester. This property may be useful in early diagnosis.