Differences in birth weight by sex using adjusted quantile distance functions.

Herein, we report results from a study of birth weight distribution among boys and girls born in Norway in 2008. As our primary interest was to detect differences in the variability between the two sexes, we used the quantile distance function to describe the difference between two distribution functions. We used an adjusted version of the quantile function to look into the relation of sex differences in birth weight conditioned on maternal age, gestational age, preeclampsia, maternal diabetes type 1, maternal smoking status, and parity. At term (⩾37 weeks of gestation), boys showed a greater variability in birth weight than did girls, and these differences were maintained in the adjusted model. We also found that maternal age and maternal smoking habits influenced both sexes equally, whereas gestational age, preeclampsia, maternal diabetes type 1, and parity influenced one sex more than the other. The adjusted quantile distance function proved efficient in analyzing and demonstrating how covariates influence sex differences in birth weight.