The Prevalence of Nonserious Events in a Cohort of Breastfed Infants

Data on baseline rates of nonserious events in breastfed infants in the general population are sparse. This results in difficulty determining if there is an increase in infant nonserious events potentially due to prescription medication exposure through human milk. In this study, we determined the prevalence of nonserious events in infants consuming human milk whose mothers reported no exposure to any prescription medications, tobacco, or recreational drugs in the previous 14 days. Between August 2014 and December 2019, 487 breastfeeding mothers without any recent exposure to prescription medications, tobacco, or recreational drugs enrolled in the Human Milk Research Biorepository at the University of California, San Diego. Participants completed a semistructured telephone interview with trained research staff and provided information on maternal and child health, breastfeeding habits, recent medication, and lifestyle exposures, and completed a standard checklist of infant adverse reactions. We found 131 (44.1%) participants reported one or more infant nonserious adverse events in the past 14 days at the time of their study interview. The most commonly reported nonserious events were rash (12.1%), irritability (9.4%), constipation (7.8%), poor sleep (7.1%), and fever (6.3%). These baseline frequencies provide a benchmark for rates of recent nonserious events in breastfed infants in the general population. These data can be used as a reference point for studies that examine adverse events in breastfed infants following maternal use of prescription medications or exposures due to other lifestyle habits such as tobacco or other substances. Clinical Trial Registration Number: NCT05553743.