Differences in maternal-newborn ABO blood groups and risk of serious infant infection.

BACKGROUND:During pregnancy, various maternal IgG antibodies are transferred to the developing fetus, some of which may protect the newborn against infection. If a mother and her fetus have different ABO blood groups, then transferred maternal antibodies may plausibly protect the infant against infection. AIM:To determine if maternal-newborn ABO blood group incongruence vs. congruence is associated with a lower risk of serious infection in the infant. DESIGN:Retrospective population-based cohort. METHODS:We used linked patient-level datasets for all singleton hospital livebirths from 2008-2022 in Ontario, Canada, with known maternal and newborn ABO blood groups. We used a dichotomous exposure state, either ABO blood group congruent (N = 114,507) or incongruent (N = 43,074). The main outcome of interest was the risk of serious infant infection within 27 days, and from 28-365 days, after birth. Cox proportional hazard models generated hazard ratios and 95% confidence intervals, and were adjusted for maternal age, world region of origin, residential income quintile, and gestational age at birth. RESULTS:Relative to maternal-newborn congruency, incongruent ABO blood group was associated with aHR of 0.88 (95% CI 0.80 to 0.97) for serious neonatal infection within 27 days of birth, and 0.93 (95% CI 0.90 to 0.96) for serious infection between 28-365 days after birth. CONCLUSIONS:Maternal-newborn ABO incongruence may be associated with a lower relative risk of a serious infant infection within 27 days, and from 28 to 365 days, after birth.