To determine the variation of cerebellar fissure with gestational weeks in normal fetuses and to establish the numeric reference range for fetal cerebellar fissure at 16-32 weeks.

From June 2019 to December 2020, 644 singleton fetuses with no structural abnormalities diagnosed by prenatal ultrasound were selected as study subjects at Shenzhen Maternal and Child Health Hospital, and divided into two groups: fetuses at 12-15 weeks of gestation and those at 16-32 weeks. The primary fissure and horizontal fissure in two-dimensional images were observed, the number of cerebellar fissures at 16 to 32 weeks of gestation counted, and the morphological changes analyzed. Forty fetuses were randomly sampled and tested for repeatability between two observers. The normal numeric reference range for cerebellar fissure between 16 and 32 weeks of gestation was established. The correlation between the number of cerebellar fissures and gestational age was analyzed by Spearman correlation, and fitting equations were then established.

There was no significant difference in the repeatability test between the two observers. The scatter plots showed that the number of cerebellar fissures were positively correlated with gestational age (r=0.863, 0.698, 0.831, and 0.932, P＜0.001). Quadratic polynomial regression equations were each fitted to the models. The regression equations for the number of cerebellar fissures in three different regions and the total number of fissures were Y=0.974X-0.014X ² -12.65, Y=0.362X-0.005X ² -4.843, Y=-0.125X+0.006X ²+0.285, and Y=1.800X-0.024X ² -22.904, respectively.

Prenatal ultrasound can be used to observe and evaluate the development of fetal cerebellar fissures. The numeric reference range and morphological changes of the normal fetal cerebellar fissures may be useful for prenatal evaluation of the development of the cerebellar cortex.