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Fetal cephalometry by ultrasound as a screening procedure for the prenatal detection of Down's syndrome
Insights
The cephalic index, a measure of head shape, is higher in children with Down syndrome. However, this difference is not detectable by ultrasound in mid-gestation fetuses, suggesting it
Area of Science:
- Prenatal diagnosis
- Fetal medicine
- Genetics
Background:
- Infants and children with Down syndrome exhibit a higher cephalic index (CI) compared to unaffected individuals.
- The cephalic index, defined as the ratio of biparietal to occipitofrontal diameter, reflects fetal head shape.
Purpose of the Study:
- To investigate if the cephalic index difference observed in liveborn children with Down syndrome is detectable via second-trimester fetal ultrasound.
- To assess the utility of ultrasound cephalometry in identifying Down syndrome during mid-gestation.
Main Methods:
- Cephalic indices were calculated for 308 normal fetuses.
- Cephalic indices were also calculated for eight fetuses with a 47, +21 karyotype (Down syndrome).
- Ultrasound measurements of biparietal and occipitofrontal diameters were used to determine the CI.
Main Results:
- The mean cephalic index for fetuses with Down syndrome was 0.829 (SD 0.033).
- The mean cephalic index for normal fetuses was 0.825 (SD 0.042).
- The difference in mean CI between the two groups was not statistically significant and indistinguishable.
Conclusions:
- The cephalic index difference associated with Down syndrome is not detectable in mid-gestation fetuses using ultrasound.
- Ultrasound cephalometry alone is unlikely to be a reliable method for discriminating between normal and Down syndrome-affected fetuses.
- Further research may be needed to identify reliable ultrasound markers for prenatal Down syndrome detection.
Abstract:
Infants and children with Down's syndrome have a cephalic index (ratio of biparietal to occipitofrontal diameter) higher than that in normal children. To determine whether this difference is present and detectable by ultrasound measurement of the second-trimester fetal head, we calculated the cephalic indices for 308 normal fetuses and eight fetuses with a 47, +21 karyotype. The mean cephalic index in the fetuses with Down's syndrome (0.829, SD 0.033) was indistinguishable from that in the normal fetuses (0.825, SD 0.042). These data suggest that the documented difference in mean cephalic index between liveborn children with Down's syndrome and normal control children is not detectable in the mid-gestation fetus and that ultrasound cephalometry alone is unlikely to discriminate reliably between normal and affected fetuses.