Sphenofrontal distance on three-dimensional ultrasound in euploid and trisomy-21 fetuses at 16-24 weeks' gestation

Objective: To compare the distance between the sphenoid and frontal bones on three-dimensional (3D) ultrasound in euploid and trisomy-21 fetuses at 16-24 weeks' gestation. Methods: We acquired 3D volumes of the fetal profile from 80 normal and 30 trisomy-21 fetuses at 16-24 weeks' gestation. We used the multiplanar mode to obtain the mid-sagittal plane and measured the sphenofrontal distance as the shortest distance between the most anterior edge of the sphenoid bone and the lowest edge of the frontal bone. Results: In normal fetuses, the sphenofrontal distance increased linearly with gestational age, from 15.1mm at 16 weeks to 18.2mm at 24 weeks. In fetuses with trisomy 21, the mean sphenofrontal distance delta value was significantly smaller than in normal cases (-3.447mm (95% CI, -5.684 to -1.211mm); P<0.01). The sphenofrontal distance was below the 5th and 1st percentiles of the normal range in 29 (96.7%) and 27 (90.0%) trisomy-21 fetuses, respectively. Conclusions: The sphenofrontal distance is shorter at 16-24 weeks' gestation in fetuses with trisomy 21 than in normal fetuses. A reduction in the growth of the anterior cranial base contributes to the mid-facial hypoplasia observed in fetuses with trisomy 21.