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

Abstract 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 A, B or O (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 to 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 to 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 an adjusted hazard ratio of 0.88 (95% CI: 0.80–0.97) for serious neonatal infection within 27 days of birth, and 0.93 (95% CI: 0.90–0.96) for serious infection between 28 and 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.