Sex-related differences in the anteroposterior diameter of the foetal cisterna magna

To measure the anteroposterior diameter of the foetal cisterna magna and observe whether there are differences according to sex.

Three hundred and thirty-seven Chinese women with low-risk pregnancies and a singleton foetus between 22 and 38 weeks' gestational age were included in this retrospective study. Informed consent of the volunteer subjects and hospital authority approval were first obtained. Double-blinded for gender, the anteroposterior diameter of the cisterna magna of the foetuses was measured by transabdominal sonography. Magnetic resonance imaging (MRI) was used for those foetuses with mega cisterna magna. All of the foetuses were healthy by prenatal and postnatal examination, including physical and imaging examination.

The mean anteroposterior diameter of the cisterna magna of all foetuses was 8.01+/-1.79 mm. The anteroposterior diameter of the cisterna magna had no obvious correlation with the gestational age. The mean anteroposterior diameter of the cisterna magna of 179 male foetuses was 8.63+/-2.16 mm, and the mean anteroposterior diameter of the cisterna magna of 158 female foetuses was 7.87+/-1.74 mm. The size difference was statistically significant (p<0.001). In the 33 foetuses with mega cisterna magna, the number of male foetuses was greater than female foetuses, and the proportion of the foetuses with mega cisterna magna in the male group was significantly higher than the foetuses in the female group (p<0.05).

Male foetuses had slightly larger anteroposterior diameters of the cisterna magna than female foetuses. The study would be useful for creating normal range values for the cisterna magna of male and female foetuses.