Transabdominal Ultrasound Measurement of Fetal Optic Chiasm Width Across Gestational Age in an Iranian Cohort

ABSTRACT Introduction Prenatal ultrasound assessment of the fetal optic chiasm (OC) may contribute to the evaluation of midline brain structures. Regional descriptive data on fetal OC width remain limited. Methods This cross‐sectional study included 170 singleton fetuses examined between 17 weeks 6 days and 39 weeks 1 day at two tertiary hospitals. OC width was measured using the standardized three‐step transabdominal technique, and interocular distance (IOD) was recorded. Measurements were summarized descriptively across four gestational‐age groups. Associations were assessed using Pearson and Spearman correlations, linear regression, and Kruskal–Wallis tests. Results Mean OC width was 6.46 ± 1.07 mm and was positively associated with gestational age (Pearson r = 0.582, p < 0.001). The regression slope was 0.157 mm per gestational week (95% CI, 0.123–0.190). Mean IOD was 16.46 ± 2.84 mm and was also associated with gestational age ( r = 0.630, p < 0.001). Both measurements differed across gestational‐age groups ( p < 0.001). The cohort was concentrated at 32–36 weeks 6 days (54.1%). Conclusion OC width was positively associated with gestational age in this eligible ultrasound cohort. The findings provide descriptive biometric data, particularly for later gestation. Larger, more evenly distributed samples and reproducibility assessment are needed to establish clinically applicable reference values.