Objective: This study was designed to evaluate the significance of gender differences for commonly used biometric parameters obtained ultrasonographically from second-trimester euploid fetuses.
Study design: Gender-specific linear regression equations were developed for gestational age dependent and independent biometry from second-trimester ultrasonographically normal singleton euploid fetuses by use of biparietal diameters and femur and humerus lengths. Regression lines for male fetuses were compared with those for females by determining overlap of 95% confidence intervals at specific points.
Results: A total of 288 male fetuses (mean gestational age 16.7 +/- 1.0 weeks) and 251 female fetuses (mean gestational age 16.8 +/- 1.2 weeks) (not significant) were evaluated. Small statistically significant gender differences in fetal biometry were identified. The largest gender difference for gestational age-dependent parameters was a biparietal diameter difference of 1.15 mm at 21 weeks. The largest gender difference for gestational age-independent parameters was a femur length difference of 1.7 mm at a biparietal diameter of 50 mm.
Conclusion: Statistically, but not clinically, significant gender differences of small magnitude exist for second-trimester fetal biometry, suggesting that gender-specific nomograms may be of limited value.