Maternal-newborn ABO blood group congruence among consecutive births and risk of serious neonatal infection: retrospective cohort study

Background — Differing ABO blood groups between a mother and her fetus may confer a lower risk of serious neonatal infection. How sensitization in the first pregnancy influences this phenomenon in a subsequent pregnancy is unclear. Accordingly, this study determined whether maternal-newborn ABO blood group incongruence in a first pregnancy further modifies the risk of serious infection in a subsequent pregnancy marked by ABO incongruency.

Methods — This population-based retrospective cohort study used linked patient-level datasets in Ontario, Canada, from 2008 to 2022. Included were mothers with 2 consecutive live births, with recorded maternal and newborn ABO blood group data. The exposure considered both first- and second-born siblings’ ABO blood group congruency with their mother. The outcome was a serious neonatal infection within 27 days after birth. Logistic regression models generated adjusted odds ratios (aORs) and 95% confidence intervals (CIs), adjusted for gestational age at birth.

Results — Included were 14,739 mother-infant triads. Relative to maternal-newborn congruency in the second pregnancy, incongruent ABO blood groups in the second pregnancy were associated with an aOR of 0.72 (95% CI, 0.53–0.97) for a serious neonatal infection arising in the second-born infant. However, if the first and second siblings each had incongruent ABO blood groups with their mother, the aOR of serious infection in the second-born infant was not significantly lower [0.74 (95% CI, 0.52–1.06)].

Conclusions — Second-born infants whose ABO blood group was incongruent with that of their mother had a lower risk of serious neonatal infection. However, ABO incongruence from a prior birth did not modify that relation.