(864) Maternal Rates of Alloimmunization at Initiation of Pregnancy Care: Insights from a National Cohort

Hemolytic disease of fetus and newborn (HDFN) is a life-threatening disease mediated by maternal alloimmunization. Published prevalence studies of maternal antibodies in the United States (US) include single center reports but no national data. This study describes contemporary prevalence and temporal trends in alloimmunization in early pregnancy in the US.

Study Design: Red blood cell antibodies (RBC Abs) in obstetric panels during 2010-2021 were identified in a national commercial laboratory database. The Overall Cohort comprised pregnant patients screened for RBC antibodies in an initial obstetric panel; Continuity Cohort included those who had additional 3rd trimester oral glucose challenge. Data were normalized based on US Centers for Disease Control live births and weighted by year and census division to estimate the national prevalence of alloimmunization. Cochrane-Armitage tests were used to assess for alloimmunization temporal trends.

Results: Of 9,876,196 pregnancies, 1.5% screened positive for RBC Abs; 0.9% (914/100,000 pregnancies) identified and 0.6% (604/100,000) unidentified. Of identified RBC Abs, anti-D comprised 64%, corresponding to an estimated national rate of 586/100,000 pregnancies. Prevalence of other high-risk RBC Abs for HDFN included anti-E (110/100,000), anti-K (68/100,000), and anti-c (29/100,000) (Table). Similar results were observed in the continuity cohort. There was an increasing temporal trend for all four high risk antibodies (all P < .001).

Conclusion:

Among nearly 10 million pregnancies in the US from 2010 to 2021, 1.5% screened positive for RBC Abs. Over 50% (793/100,000) had RBC Abs known to be high risk for HDFN with an increasing temporal trend. Though overall prevalence of anti-D is difficult to interpret without ability to distinguish active from passive presence, it likely remains problematic in HDFN as demonstrated by ranking second only to anti-K in critical titers. Given the severity of HDFN, new initiatives may be required to reduce alloimmunization incidence in patients of reproductive potential.