Variation of Fetal Humeral Length in Second‐Trimester Fetuses According to Race and Ethnicity

Objective. To determine the influence of race and ethnicity on the expected humeral length based on biparietal diameter measured in second‐trimester fetuses. Methods. We searched our ultrasound, obstetric, and cytogenetic databases from 1995 through 2001 for all fetuses who underwent an anatomic survey between 15 and 22 weeks' gestation. Fetuses with Down syndrome were identified and removed for separate analysis. Linear regression curves were generated for humeral length by biparietal diameter according to race and ethnicity. Analysis of variance was used to compare the mean variation of observed from expected humeral length by biparietal diameter according to race and ethnicity. Results. There were 11,278 humeral length‐by‐biparietal diameter pairs that were available for analysis in our population, including 4202 African American, 2269 Hispanic, 639 Asian, and 4168 white fetuses. Humeral length was highly correlated with biparietal diameter for each race (R2 = 0.8). There were no differences in mean variances according to race or ethnicity (P = .75). Conclusions. Race and ethnicity do not affect the mean regression line of expected humeral length by biparietal diameter among fetuses in the second trimester. Genetic sonographic norms, therefore, do not require race‐ or ethnic‐specific formulas for humeral length.