Background: Expectant parents are extremely interested in learning the gender of the fetus during the early stages of pregnancy. Yet, clinicians are also interested in identifying the gender of fetuses at increased risk of inheriting gender-dependent genetic diseases. In the presence of hereditary illnesses associated with gender, it becomes a necessity rather than an interest. Objective: The aim of the current study is to evaluate the reliability of early-trimester fetal sex diagnosis of pregnancy, as well as the relationship between anogenital distance (AGD) in the first trimester and fetal sex determination. Patients and methods: A prospective cohort study was conducted at the Department Obstetrics and Gynecology of Zagazig University Hospitals, from August 2021 to December 2022. The study included 245 pregnant women, aged between 18 and 35 years. Participants were singleton pregnancy with gestational age from 11 to 13 weeks (+6 days). The enrolled pregnant women in our study were divided into 3 groups; Group 1 included fetuses that aged 11 weeks (+6 days), Group 2 included fetuses that aged 12 weeks (+6 days), and Group 3 included fetuses that aged 13 weeks (+6 days). Result: Our research indicated no statistically significant difference between AGD in groups 2 and 3 (P=0.758), although there was a statistically significant difference between Group 1 and both Groups 2 and 3 (P<0.001), thus, both groups 2 and 3 were combined into one group. It was established that the optimal cut-off value for the merged group was 4.9mm, AUC 0.961 (P<0.000). The sensitivity was 93.41%, specificity was 86.49%, positive predictive value 89.47%, negative predictive value 91.43%, and likelihood ratio 6.91. Conclusion: This research backs the use of fetal AGD measurement as a new ultrasonographic technique signal for determining a baby's gender early on. This procedure appears to be accurate, especially after 12 weeks of pregnancy. It is recommended measuring AGD during the first trimester of early pregnancy for accurate gender prediction.