Objective To explore the developmental characteristics of width of cerebellomedullary cistern in fetus and its differences in gender.

Methods A total of 574 pregnant women who underwent routine obstetric ultrasonography were selected as study subjects. Pregnant women's age, gestational age, fetal sex and other information were collected. The fetal double parietal diameter, head circumference, transverse diameter of cerebellar hemisphere and width of cerebellomedullary cistern were measured by ultrasound. The correlation between width of cerebellomedullary cistern and fetal craniocerebral diameter as well as its developmental characteristics of different gender were analyzed.

Results The average width of cerebellomedullary cistern was (6.86±1.55) mm; the mean gestational age was (27.00±4.00) weeks; the average diameter of double top was (67.68±32.54) mm; the average head circumference was (241.78±43.93) mm; the mean transverse diameter of cerebellar hemisphere was (29.36±7.72) mm. The width value of cerebellomedullary cistern was positively correlated with gestational age, double parietal diameter, head circumference and transverse diameter of cerebellar hemisphere, and had the highest correlation with head circumference (P < 0.05), and the correlation coefficients were 0.269, 0.105, 0.309 and 0.189, respectively. Head circumference and transverse diameter of cerebellar hemisphere had significant effects on the width of cerebellomedullary cistern (P < 0.05). The width of cerebellomedullary cistern increased with gestational age before 30 weeks, but did not change too much at 30 to 40 weeks. The correlations between cerebellomedullary cistern width and gestational age, biparietal diameter, head circumference and transverse diameter of cerebellar hemisphere increased at 17 to 30 weeks, and the correlation coefficients were 0.552, 0.549, 0.567 and 0.416, respectively. The width of cerebellomedullary cistern was linearly correlated with head circumference and increased with head circumference (R²=0.321). The average width of cerebellomedullary cistern in males was (7.03±1.60) mm, which was significantly more than (6.69±1.47) mm in females (P < 0.05).

Conclusion When determining the normal range of cerebellomedullary cistern width, the changes rules of cerebellar bulbar cisterna in pregnant women before 30 weeks of pregnancy can be referred, and the fetal sex difference can be considered.