Prenatal Antibiotics and Breast Milk / Neonatal IgA

In a human cohort of women and their neonates, the investigators aim to evaluate the absolute amount of IgA in maternal breast milk and in neonatal feces in the presence (N=41 mother/infant pairs) or in the absence (N=41 mother/infant pairs) of exposure to prenatal ABX during the last period of pregnancy. Moreover, the investigators aim to evaluate, both in maternal breast milk and in neonatal feces, the composition of microbiota, and the proportion and composition of the IgA-coated and not-IgA- coated fractions of microbiota, by means of fluorescence-activated cell sorting (FACS) coupled with 16S rRNA sequencing of bacteria. Finally, the investigators will measure the concentration of the chemokine CCL28 on maternal serum and breast milk, as a soluble marker of activity of the entero-mammary pathway that is known to drive the migration of IgA producing plasma- cells from maternal mesenteric lymph nodes to the mammary gland. All the analysis will be performed in mother-infant dyads with exclusive breastfeeding. Breast milk/serum/feces collection and analysis will be repeated at the following timepoints: 1. during the first week of neonatal life 2. at 1 month of life 3. at 3 months of life 4. at 8-12 months of life (or at the time of breastfeeding interruption), after the introduction of solid food in the infant's diet.