Perinatal outcomes in RhD-negative pregnant women in Japan.

Managing RhD-negative pregnancies is vital for preventing hemolytic disease of the fetus and newborn, which occurs when RhD-negative mothers develop anti-D antibodies after exposure to RhD-positive fetal blood. This retrospective cohort study evaluated the proportion of RhD-negative pregnancies and newborns in Japan by assessing current management practices and outcomes. This study included RhD-negative pregnant women who delivered at 22 weeks or later at 47 Japanese facilities between April 2018 and March 2023. Pregnancies with unknown newborn RhD status were excluded. Data were obtained from medical records. Among the 1088 RhD-negative women, 1062 met the inclusion criteria. RhD-negative pregnancies comprised 0.71% of the total cohort, with 8.7% RhD-negative newborns. Anti-D immunoglobulin was administered in 96.5% of pregnancies, with a maternal spontaneous sensitization rate of 0.6% before 28 weeks and no sensitization detected from 28 weeks to postpartum. Sensitized RhD-negative women had higher cesarean section, preterm delivery, and neonatal hemolytic anemia rates than the non-sensitized group, leading to increased neonatal intensive care unit admissions. Despite the low incidence of RhD-negative pregnancies, this study underscores the need for tailored management strategies, suggesting that non-invasive prenatal diagnosis of fetal RhD status could prevent unnecessary anti-D immunoglobulin administration, improving outcomes and resource utilization in Japan.