The Effects of Delivery Method and Infant Feeding on Weight Gain during the First Year of Life

Abstract

Rapid weight gain in the first year of life sets the growth trajectory and is a risk factor for obesity. New evidence suggests that obesity in mice and humans is characterized by altered gut bacteria, compared to their lean counterparts. Two early factors that influence gut bacteria are delivery method and infant feeding. Since delivery method and infant feeding affect the initial colonization of gut bacteria, and gut bacteria is associated with obesity, the purpose of my dissertation is to study the effects of delivery method, breast feeding intensity, and their joint effects on infant growth in the first year of life. This is a secondary analysis of data from the Infant Feeding Practices Study II (IFPS), a longitudinal follow-up study of new mothers conducted by the US Food and Drug Administration from 2005-2006. Participants were from a consumer panel of 500,000 households. Survey questionnaires were sent to pregnant women 10 times at regular intervals during the year after they gave birth. All participants were women >18 years of age who delivered a healthy infant. Delivery methods were reported as spontaneous vaginal, induced vaginal, planned C-section and emergency C-section. Breastfeeding intensity was reported at months 1-7, 9, 10 and 12 months. Emergency C-section and induced vaginal deliveries were associated with lower breastfeeding intensity, compared to women who had spontaneous vaginal delivery. However, no differences in breastfeeding intensity were found between planned C-section and spontaneous vaginal delivery. In the second study, infants who received 0% and 1-49%% milk feeds from formula gained more weight than those fed 100% breast milk. The adjusted weight gain of these 2 groups was also higher than a cut-off point for risk of later obesity. Finally, weight gain was similar for infants born by vaginal deliveries and C-sections. Infants fed at least 50% breast milk gained less weight after 5 months of age. Joint effects of delivery method and breastfeeding intensity did not significantly affect infant weight gain. All three studies provide suggestions for future research needed to fully understand how delivery method and infant feeding affect gut colonization which in turn may affect infant development.