Is Size of Cisterna Magna Related to the Fetal Gender and Gestational Age?

Background: The cisterna magna (CM) is a large subarachnoid cerebrospinal space located between the caudal aspect of the cerebellum and the medulla oblongata, draining the fourth ventricle. This study aimed to assess the relationship between the anteroposterior diameter of the CM, gestational age, and fetal gender. Methods: A prospective observational study was conducted on 450 Egyptian pregnant women between 20 weeks 0 days and 39 weeks 6 days of gestation, all with singleton pregnancies without detectable structural abnormalities via prenatal ultrasound. Results: Participants' ages ranged from 16 to 42 years (mean ± SD: 27.5 ± 6.08 years). Of the cohort, 51.33% resided in urban areas and 48.67% in rural areas; 45.78% were illiterate and 54.22% were educated. CM size ranged from 0.3 to 1.0 cm (mean ± SD: 0.72 ± 0.17 cm) and was significantly larger in male fetuses than in female fetuses (P < 0.001). No significant difference was observed between 20–23 and 24–27 weeks; however, CM size was significantly greater at 28–31, 32–35, and 36–39 weeks compared with 20–23 weeks (P < 0.001). CM size positively correlated with gestational age (r = 0.338, P = 0.001). Conclusion: CM size increases with advancing gestational age and shows a statistically significant association with fetal gender. These results suggest that both variables should be considered when interpreting CM measurements during routine prenatal assessments to improve diagnostic accuracy.