Sex differences in preterm nutrition and growth: the evidence from human milk associated studies

Sexual dimorphism of the fetus manifests itself even during pregnancy. Preterm births are more common in pregnancies with male fetuses. Intrauterine and postnatal growth nomograms are sex-specific. The human milk composition in term infants appears to be sex-specific. Early nutrition has sex-specific effects and neurodevelopmental outcomes. A large same-sex twin study suggests that a mother’s own milk (MOM) provides sex-specific growth advantages probably related to the calibration of a mother’s milk based on her newborn’s sex. Formula composition does not vary with infant sex, which may be one reason why body composition data favors the use of MOM over formula. However, given the lack of data on this subject, we need more detailed information on how the sex-specific micronutrients in MOM influence infant well-being. We also need more information to ascertain the sex differences in infants’ macronutrient requirements, such as whether preterm females have higher fat requirements and preterm males have higher protein requirements for optimal growth and neurodevelopmental outcomes. This information may also influence milk banking and the use of donor human milk (DBM). Further research may help us determine if we should provide sex-specific DBM to those preterm infants who cannot get their MOM.