['To elucidate whether the risk of macrosomia, large for gestational age (LGA) and small for gestational age (SGA) is influenced by maternal body mass index and glucose tolerance differently in male and female fetuses.', 'A population study was conducted in 16 general hospitals from the Spanish National Health Service that included 9270 consecutive women with singleton pregnancies and without a former diagnosis of diabetes mellitus who delivered 4793 male and 4477 female newborns. Logistic regression analyses were performed to predict the effect of body mass index (BMI) category and glucose tolerance on macrosomia, large for gestational age newborns (LGA) and small for gestational age newborns (SGA) Separate analyses according to foetal sex were carried out for each outcome. The results were adjusted for maternal age, gestational age and pregnancy-induced hypertension.', 'There were significant differences between males and females in the percentage of infants who had macrosomia, LGA or SGA. Maternal BMI category was positively associated with the risk of macrosomia and LGA in both male and female newborns. In addition, there was a negative association between maternal BMI and SGA that only reached significance in males. In contrast, gestational diabetes was only a predictor of macrosomia exclusively in male fetuses (OR 1.67, 95% CI 1.12 to 2.49)'] Does maternal glucose tolerance status influence the risk of macrosomia in male but not in female fetuses?