Do prenatal antibiotics weaken breast milk immunity? A new study aims to find out

Could antibiotics taken during pregnancy weaken the protective power of breast milk? A new study will explore whether prenatal antibiotic exposure reduces key immune factors in breast milk, potentially altering a newborn’s gut microbiome and immune resilience.

Study Protocol: Effect of prenatal antibiotics on breast milk and neonatal IgA and microbiome: a case-control translational study protocol. Image Credit: Lolostock – Apex Studios / Shutterstock

In a recent study protocol published in the journal Pediatric Research, a team of researchers in Milan, Italy, proposed to evaluate the impacts of maternal antibiotic (ABX) treatment on breastmilk composition and their babies' gut microbial health and immune system functionality. Their previous research in murine models has revealed that ABX treatment alters pups' unique intestinal microbial composition, reduces IgA levels, and impairs gut immune defense. While these findings suggest a possible effect in humans, the proposed study aims to confirm whether similar gut microbial and immune alterations occur in human neonates.

To verify this hypothesis, they propose to recruit and follow for one year two cohorts of women (and their babies; 41 pairs each) who were either exposed to at least seven consecutive days of ABX treatment (cases) or had no antibiotic exposure during pregnancy (controls) during the final stages of their pregnancy. Their investigations will include estimations of breast milk immunoglobulin A (IgA), gut microbiota, and neonatal fecal microbiota using ELISAs, magnetic cell sorting, and shotgun genomic techniques. Their findings will help inform mothers and clinicians of the impacts of antibiotic treatment on neonatal health.

Background

The relationship between symbiotic microbiota and the immune system is complex and bidirectional. Decades of research have shown that the composition of symbiotic microbiota (e.g., gut microbes) substantially alters immune system functioning. In turn, host mucosal secretory components (e.g., secretory immunoglobulin As [sIgAs]) have been found to shape microbiota composition.

"…it is known that humans deficient in IgA have a unique intestinal microbiota characterized by the expansion of Enterobacteriaceae, akin to IgA-deficient murine strains where Enterobacteriaceae and segmented filamentous bacteria (SFB) are predominant."

Recent studies by the current team and others suggest that mothers' breast milk components (immune and microbiota) shape and seed their offspring's microbial assemblages while simultaneously preventing gut bacterial translocation. Mother's milk has also been shown to significantly contribute to babies' lifelong neurodevelopmental outcomes, highlighting its importance.

Separately, studies have found that antibiotic (ABX) treatment can significantly alter gut and lung microbiota composition. While these alterations are usually temporary and recover in adults, ABX-induced dysbiosis substantially weakens immune system performance. Alarmingly, ABX administered during the neonatal period has been reported to trigger short- and long-term medically adverse events, including atopy, obesity, and necrotizing enterocolitis (NEC).

Unfortunately, it remains unknown if ABX treatment in pregnant or breastfeeding women can adversely impact their offspring's health by disrupting the entero-mammary pathway and reducing breast milk immune function.

About the study

The proposed study seeks to address these knowledge gaps and provide mothers and clinicians with the information required to make informed ABX choices. It hypothesizes that prolonged ABX consumption may reduce breast milk quantity and IgA polyreactivity, especially if administered during the final stages of pregnancy.

"This reduction could be caused by an impaired functionality of the so-called 'entero-mammary pathway,' through which plasma cells migrate to the mammary gland from the mesenteric lymph nodes driven by the gradient of the epithelial chemokine CCL28 produced by the mammary gland itself."

This hypothesis is linked to a second hypothesis that maternal intestinal dysbiosis may prevent IgA-producing plasma cells from sufficiently migrating to mammary glands, thereby reducing neonatal fecal IgA and resulting in neonatal intestinal dysbiosis.

The proposed study will be conducted as a collaborative effort between the current research team and the Mucosal Immunology and Microbiota laboratory of IRCCS Istituto Clinico Humanitas, Rozzano (Milan), Italy. Experimental assays will be carried out at the Department of Woman, Child, and Newborn of Fondazione IRCCS Ca' Granda—Ospedale Maggiore Policlinico of Milan. The study design is a case-control study, each of which will comprise 41 mother-offspring pairs.

Inclusion criteria will limit participant intake to only adults (18-40 years) who provide informed consent to potential antibiotic treatment (minimum of seven consecutive days) during the final stages of pregnancy (minimum 32 weeks of gestation). Participants unwilling to breastfeed their offspring for at least as long as possible during the first year following delivery will be excluded from the study. Demographic and medical data of participants will be obtained from electronic health records.

The study proposes several rounds of follow-up during the first week after delivery, at the first month after delivery, and then again at 3 months and 8–12 months (after solid food introduction). At the 8–12-month follow-up, researchers will also assess infants' neurodevelopment using the Ages and Stages Questionnaire (ASQ-3), measuring communication, motor skills, problem-solving, and social behavior. Study data collection will include breast milk collection and babies' feces collection at each follow-up time point.

Investigative procedures will include Enzyme-Linked Immunosorbent Assays (ELISAs) for breastmilk IgA quantification and Chemokine CCL28 estimation, magnetic-activated cell sorting (MACS) of babies' feces (to separate IgA-coated and non-coated microbiota), and shotgun metagenomics sequencing (Illumina HiSeq 2500 platform) for bacterial characterization.

To compare results obtained from cases and controls, t-tests will be used for normally distributed data, Mann-Whitney tests will be used for non-normally distributed data, and repeated-measures ANOVA will be applied for longitudinal comparisons.

Study importance and conclusions

The study protocol will illuminate the interplay between immune system functionality and gut microbial dysbiosis while highlighting the impacts of ABX consumption on neonatal health. It will provide clinicians and new mothers with the knowledge required to make informed decisions about administering ABX treatment and direct the choice of the ABX itself.

By identifying how prenatal antibiotics impact breast milk IgA, microbiota, and neonatal immune development, the study will also inform future clinical guidelines and highlight potential risks associated with prolonged ABX use before delivery.