Why does mode of conception affect early breast-feeding outcomes? A retrospective cohort study

Background: Women who conceived through Assisted Reproductive Technology (ART) may experience poorer breast-feeding outcomes compared to women who conceived naturally; nevertheless, the mechanism of this relationship has not been explored. This study aimed to examine the effect of mode of conception on breast-feeding outcomes during the first two months postpartum and identify the potential pathways for this relationship. Methods: : A retrospective cohort study was conducted in a sample of 5,474 women with live births using hospital administrative data from January 2014 through December 2018. Participants were classified by mode of conception as follows: fertile women who conceived naturally (fertile women; n =4,363), women with infertility who conceived naturally (sub-fertile women; n =706), and women with infertility who conceived through ART (women with infertility; n =405). The patterns of infant feeding were acquired at hospital discharge, the first week, the first month, and the second month postpartum. Binary and multinomial logistic regression and causal mediation analyses were performed. Results: : Infertile and sub-fertile women had 34% (95% CI 1.03, 1.73) and 60% (95% CI 1.11, 2.31) increased risks of introducing formula prior to the first week postpartum, respectively, and 31% (95% CI 1.01, 1.70) and 59% (95% CI 1.10, 2.31) higher risks of exclusive breastfeeding for less than one week during the first two months postpartum, respectively, compared to fertile women. The relationships were mediated through delivery complications, multiple gestations, preterm delivery, low birth weight, and admission to neonatal/paediatric intensive care units (NICU/PICU). The path with the highest proportion mediated was through multiple gestations (60.47% for infertile women) and admission to NICU/PICU (68.60-72.61%). The effect of mode of conception on breastfeeding outcomes was not significant in cases of no maternal and infant morbidities. Conclusions: : During the first two months postpartum, infertile and sub-fertile women both had short duration (<7 days) of exclusive breastfeeding and introduction of formula prior to the first week postpartum. The relationships were mainly mediated through multiple gestations and admission to NICU/PICU. Designing programmes to reduce adverse maternal and infant health events, like a single embryo transfer policy, is suggested to improve perinatal outcomes, together with the following breast-feeding outcomes.