Predictive value and reference ranges of anogenital distance for determining fetal gender in the first trimester: A retrospective cohort study

Objectives: To assess the usefulness of sonographically measured anogenital distance (AGD) in predicting fetal gender in Saudi fetuses during the first trimester and to provide normal reference centiles for AGD.

Methods: A retrospective cohort study was conducted at King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia between November 2020 and May 2021. The ultrasound scans of 313 singleton pregnancies between 11-13 plus 6 gestational weeks and their gender-at-birth were collected. Anogenital distance was measured from the inferior base of the genital tubercle to the rump. Binominal logistic regression and receiver operating characteristic curves (ROC) evaluated the predictive performance of AGD for determining fetal gender.

Results: There was a significant difference of approximately 15% in mean AGD between female (5.92 mm [95% CI= 6.70, 6.14]) and male (6.80 mm [95% CI= 6.61,7.00]) fetuses (p<0.001). Anogenital distance significantly correlated with gestational age (r=0.573, p<0.001) and crown-rump length (r=0.562, p<0.001). The logistic regression determined AGD as a significant predictor of fetal gender (p<0.001). However, ROC analysis showed that overall accuracies were low at 68% (p=0.001) for 11 weeks, 70% (p<0.001) for 12 weeks, and 64% (p=0.017), and for 13 weeks. The average AGD of our Saudi cohort was longer than what the literature reported from other populations.

Conclusion: The first-trimester ultrasound evaluation of AGD was feasible and reliable. It showed a difference between the genders but did not yield high predictive accuracy. Future research should consider racial factors when evaluating AGD.