Aim: To evaluate the accuracy of ultrasound in determining the phenotypic foetal gender in all three trimesters.

Study design: Cross sectional study.

Place and duration of study: Department of Diagnostic Radiology Combined Military Hospital Lahore from 1st January 2020 to 30th April 2020. Methodology: Three hundred and seventy two patients in the inclusion criteria were selected. Ages of patients, gestational ages of foetuses and their genders were determined according to the ultrasonographic signs using ultrasound examination. Patients were contacted 3 weeks after the estimated date of delivery and phenotypic sex recorded.

Results: Mean age was 34 years. Median gestational age was 21 weeks 3 days. Accuracy of gender determination by ultrasound in 1st, 2nd and 3rd trimesters was 62%, 97% and 95% respectively. Sensitivity and specificity of ultrasound in 1st trimester for males are 66% and 72%; and for females are 72% and 66% respectively. Positive and negative predictive values for male are 69% and 71%; and for female are 71% and 69% respectively. Sensitivity and specificity of ultrasound in 2nd trimester for males are 95% and 100%; and for females are 100% and 95% respectively. Positive and negative predictive values for male are 100% and 94%; and for female are 94% and 100% respectively. Sensitivity and specificity of ultrasound in 3rd trimester for males are 94% and 96%; and for females are 96% and 94% respectively. Positive and negative predictive values for male are 97% and 93%; and for female are 93% and 97% respectively.

Conclusion: There is a high accuracy of ultrasound in determination of fetal gender in second and third trimesters. Keywords: Ultrasound, Gender, Trimester, Sensitivity, Specificity, Predictive Value