Nomogram of the width, length, and area of the fetal optic chiasm according to gestational week

Using transabdominal 2D ultrasonography, we aimed to establish nomograms for fetal optic chiasm (OC) width, length, and area between 16-37 weeks of gestation.OC measurements were performed by a resident and a perinatologist. An agreement was evaluated using intraclass correlation coefficients (ICCs) with 95% confidence intervals. Then, nomogram tables of OC width, length, and area measurements were derived using these measurements. A strong positive correlation was found between OC measurements and gestational week (GW) (r=0.873 for width, r=0.827 for length, r=0.863 for area; p<0.001). The regression equations obtained were: OC width=1.164+0.206×GW, OC length=0.072+0.180×GW, OC area =-25.226+2.228×GW. Interobserver agreement was high, with ICC values of 0.798 for width, 0.705 for length, and 0.758 for area, indicating consistent measurements between observers.This is the first study to establish normative data and nomograms for OC dimensions. Our findings confirm that OC width, length, and area increase linearly with advancing gestation. The high interobserver reliability suggests that these measurements can be reliably used in clinical practice and future research.