The Frequency of Severe Hemolytic Disease of the Fetus and Newborn Caused by Red Blood Cell Alloantibodies Undetected at the Antibodies Screening in the First Trimester: A Prospective Study.

Introduction: The aim of this study was to investigate the clinical consequences of anti-D and non-anti-D antibodies undetected at screening in the first trimester for hemolytic disease of the fetus and newborn (HDFN). Methods: This prospective study (conducted from 2010 to 2024) included pregnant women with negative first-trimester antibody screening for red blood cell (RBC) antibodies but positive later in pregnancy for clinically significant antibodies anti-D and non-anti-D. We analyzed the incidence of antibodies, DAT of the newborn, and the treatment and outcomes of HDFN. Results: In study period, 61,200 pregnant women were tested, of which 11,000 were RhD-. In 32 cases, anti-D antibodies were initially detected at the repeated screening (28th/34th week of pregnancy or to 24 h post-delivery). All women have given birth to D+ child, of which 50% had a positive DAT. Four of them had early jaundice. In two cases, blood transfusion was required due to anemia. The incidence of anti-D antibody undetected at first trimester was 29/10,000 in D- women. Anti-D antibody caused severe HDFN in 1.8/10,000. Non-anti-D antibodies have been detected on repeated screening in seven cases, anti-c (N = 5), anti-E (N = 1), anti-C (N = 1). All seven neonates were antigen positive, three of which had positive DAT due to anti-c antibodies. The neonates with positive DAT had early jaundice and needed phototherapy, but there were no cases of severe HDFN in this group. Conclusion: First-trimester screening for RBC antibodies detected all cases of severe HDFN caused by non-anti-D antibodies out of 61,000 pregnant women tested.