Breastfed infants who receive formula in the hospital are more than twofold more likely to wean during the first year, compared with infants who are exclusively breastfed, according to research published online in Pediatrics.

Baby drinking formula from a bottle. patrisyu/Thinkstock

The finding is based on an analysis of data from over 8,000 infants in the Minnesota Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). The researchers used propensity scoring methods to match breastfed infants who received in-hospital formula to those who were exclusively breastfed. The researchers adjusted for potential confounders such as maternal age, cultural identity, marital status, education level, smoking, body mass index, diabetes mellitus, previous breastfeeding experience, and infant gestational age and birth weight.

“Our study strengthens the evidence that formula supplementation of breastfed infants negatively affects breastfeeding duration,” said Marcia Burton McCoy, MPH, of the Minnesota Department of Health’s WIC, and Pamela Heggie, MD, of the University of Minnesota in Minneapolis. “This finding has important clinical implications because breastfeeding duration has been shown to have a significant impact on numerous health outcomes, with a dose-response protective effect for sudden infant death syndrome, infection in infancy, and childhood obesity.”

Breastfeeding has various medical and neurodevelopmental benefits, and “even brief exposure to formula alters the infant microbiome long-term and increases the risk of allergy at 2 years of age,” the authors said.

In their study, one analysis that included 5,310 infants assumed that all bias was controlled through matching. A second, more conservative analysis that corrected for medically necessary supplementation included 4,836 infants. The researchers used data about in-hospital feeding which the Minnesota WIC staff collected in 2016 during WIC appointments.

In the first analysis, the hazard ratio of weaning across the first year was 6.1 among breastfed infants exposed to in-hospital formula feeding. In the second analysis, the hazard ratio was 2.5.

In-hospital formula feeding often leads to continued supplementation after discharge and may directly affect milk supply, Ms. McCoy and Dr. Heggie said. In-hospital formula feeding “is seldom medically necessary and, with rare exceptions, not medically indicated when the mother’s own milk or pasteurized donor milk is available.”

The study population was of lower income and more culturally diverse, compared with the general population, which may limit generalizability of the results, the authors noted.

With propensity scoring, the investigators found an association between in-hospital formula feeding and early weaning that “is analogous to previous estimates” that relied on more traditional observational methods, Lori B. Feldman-Winter, MD, MPH, professor of pediatrics at Cooper Medical School of Rowan University in Camden, N.J., and Ann L. Kellams, MD, professor of pediatrics at the University of Virginia in Charlottesville, said in an accompanying editorial.

“Maternal conditions such as obesity ... previous breast surgery, infertility, polycystic ovarian syndrome, and breast anomalies may lead to difficulties in establishing and maintaining sufficient milk supply as well as affect duration of continued breastfeeding,” the editorialists said. “Cultural, racial, and ethnic factors are also potential nonmedical reasons for breastfeeding supplementation.” In addition, implicit biases of health care practitioners may influence breastfeeding outcomes.

“The article by McCoy and Heggie gives us a compelling reason to avoid unnecessary supplementation, but there are also significant consequences of missing suboptimal intake in the newborn,” Dr. Feldman-Winter and Dr. Kellams emphasized. “Future research should be focused on methods of identifying both women and infants at risk for suboptimal intake, biological consequences of early formula supplementation, and best methods to preserve exclusive breastfeeding or human milk feeding.”

The study authors and the editorialists had no relevant financial disclosures.

SOURCES: McCoy MB et al. Pediatrics. 2020 Jun 9. doi: 10.1542/peds.2019-2946; Feldman-Winter LB and Kellams AL. Pediatrics. 2020 Jun 9. doi: 10.1542/peds.2020-1221.