(HealthDay News) – For Rhesus D negative women with Rhesus D positive fetuses, half of all sensitizations occur in the first pregnancy, with most women developing anti-D antibodies during the second or third trimester, according to a study published online June 11 in Acta Obstetricia et Gynecologica Scandinavica.

Eleonor Tiblad, MD, from the Karolinska University Hospital in Stockholm, and colleagues conducted a retrospective cohort study to examine the timing of Rhesus D immunization in pregnancy and consequences for the index pregnancy and subsequent pregnancies. Data were used from the Swedish Medical Birth Register and National Perinatal Quality Register. Two hundred ninety Rhesus D immunized women were included.

The researchers found that for 51% of the women, sensitization occurred with the first-born child, and for 33%, with the second child. In 73% of women, anti-D antibodies developed during the second or third trimester, while for 21% they developed at term or after delivery. 56% of the neonates required treatment for hemolytic disease of the fetus and newborn in subsequent pregnancies.

“Based on our study, at least half of the cases could potentially have been avoided by routine antenatal anti-D prophylaxis in the beginning of the third trimester,” the authors write. “To optimize the beneficial effects of new prevention programs, we propose providing anti-D prophylaxis in gestational week 28–30 selectively to all Rhesus D negative women with Rhesus D positive fetuses.”

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