The development of gut microbiota and the immune system during the first months of life may be influenced by antibiotic use during pregnancy, according to research conducted at Humanitas. This effect appears to occur via breast milk. The study, which is currently limited to murine models, will require confirmation in human subjects

Antibiotic administration during pregnancy reduces levels of specific antibodies in breast milk, potentially impacting the newborn’s immune defenses. These antibodies, known as IgA, are transmitted through breastfeeding, and they contribute to the protection of infants from intestinal infections, shape gut microbiota composition and support immune system development.

The findings come from a study led by Prof. Maria Rescigno, Vice Rector for Research at Humanitas University and Deputy Scientific Director for Basic Research at Humanitas Research Hospital. The research was conducted in collaboration with Carlo Pietrasanta, researcher at the University of Milan and physician in Neonatology and Neonatal Intensive Care at the Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan.

Published in Cell Host & Microbe, the study indicates that antibiotic treatment during gestation could cause, in the first weeks of life, a higher risk of intestinal infections and bacterial translocation from the gut into the bloodstream—a condition that, in severe cases, can lead to neonatal sepsis. This increased vulnerability is linked to reduced levels of IgA in breast milk, rather than direct antibiotic effects in utero. The findings emphasize the crucial role of breastfeeding in the protection of neonates from infections.

The researchers also explored strategies to restore balance in the developing immune system and enhance resistance to neonatal infections. For example, they tested an enzyme called apyrase, which stimulates IgA production in lactation, as well as breast milk donated from subjects not exposed to antibiotics.

“If confirmed in humans, these findings could open new avenues for managing at-risk newborns. Monitoring IgA levels in breast milk could help identify vulnerable infants, particularly in cases of prematurity. Additionally, strategies such as supplementing breast milk with IgA or using fermented formulas could provide essential immune support,” explains Carlo Pietrasanta, the study’s first author.

The next step involves validating these findings—obtained from murine models—in clinical contexts, with the ultimate goal of translating them into protective and predictive strategies for managing neonatal infections. “Our research highlights the complex and vital connection between microbiota and immunity, especially during early development,” says Maria Rescigno, who coordinated the study. “More importantly, it represents a first step toward better balancing the benefits of antibiotics—often indispensable during pregnancy—with the need to minimize potential unintended consequences.”