Sexual Dimorphism in Preterm Milk: A Step Toward the Individualized Fortification of Mother’s Own Milk?

<i>Introduction:</i> Several factors can affect the composition of a mother's milk, including the infant's sex, gestational age, and single or twin delivery. We aimed to determine the association of the offspring's sex with the macronutrient and energy content in preterm milk, during the first six weeks postpartum. <i>Methods</i>: This is a retrospective, monocentric, cohort study of lactating mothers who delivered before 37 weeks at a referral tertiary maternity. A mid-infrared human milk analyzer was used. <i>Results:</i> From 174 mothers, 360 milk samples were obtained. In the milk for singletons, the mature milk for females was significantly richer in total energy, fat, and protein than the milk for males; in advanced lactation, the milk for males was richer in protein than the milk for females. The transitional milk for male twins was significantly richer in fat and energy than the milk for male singletons; mature milk for male twins was richer in energy, carbohydrates, and protein than the milk for singletons. The mature milk for female twins during the fourth week postpartum was significantly richer in fat and total energy than the milk for singletons. <i>Conclusions:</i> This study provides information on how the number of delivered fetuses and the infant's sex affects the composition of preterm milk.