Rhesus D alloimmunization in pregnancy from 1996 to 2015 in Iceland: a nation-wide population study prior to routine antenatal anti-D prophylaxis.

BACKGROUND: Rhesus D (RhD) incompatibility is still the most important cause of hemolytic disease of the fetus and newborn (HDFN) worldwide. The aim of this study was to investigate the incidence, causes, and consequences of anti-D alloimmunizations in pregnancy in Iceland, prior to implementation of targeted routine antenatal anti-D prophylaxis (RAADP) in 2018. STUDY DESIGN AND METHODS: This was a nation-wide cohort study of 130 pregnancies affected by RhD alloimmunization in Iceland in the period from 1996 through 2015. Data were collected from transfusion medicine databases, medical records, and the Icelandic Medical Birth Register. RESULTS: Of 130 RhD alloimmunizations, 80 cases (61.5%) represented new RhD immunization in the current pregnancy. Sensitization was discovered in the third trimester in 41 (51.3%) and occurred in the first pregnancy in 14 cases (17.5%). The most likely causative immunization event was the index pregnancy for 45 (56.25%), a previous pregnancy/birth for 26 (32.5%), abortion for 3 (3.75%), and unknown for 6 women (7.5%). Higher anti-D titers were associated with shorter gestational length, cesarean sections, positive direct antiglobulin test (DAT), and severe HDFN. Intrauterine transfusion (IUT) was performed in five pregnancies (3.8%), and 35 of 132 (26.5%) live-born neonates received treatment for HDFN; 32 received phototherapy (24.2%), 13 exchange transfusion (9.8%), and seven simple blood transfusion (5.3%). CONCLUSION: In about half of cases, RhD alloimmunization was caused by the index pregnancy and discovered in the third trimester. Thus, the newly implemented RAADP protocol should be effective in reducing the incidence of RhD immunization in Iceland in the future.

Red blood cell alloimmunization in pregnancy during the years 1996-2015 in Iceland: a nation-wide population study.

BACKGROUND: Red blood cell (RBC) alloimmunization during pregnancy is still a major problem. Historically, anti-D antibodies are most likely to cause severe hemolysis, but other antibodies are also important. In Iceland, postnatal RhIg prophylaxis was implemented in 1969, universal RBC antibody screening was implemented in 1978, but antenatal RhIg prophylaxis is not yet routine. STUDY DESIGN AND METHODS: This nation-wide population study gathered data on alloimmunized pregnancies in Iceland between 1996 and 2015. Blood bank alloimmunization data were linked to Icelandic Medical Birth Registry data. RBC antibodies were classified as either clinically significant or clinically nonsignificant. RESULTS: In total, 912 positive antibody screens from 87,437 births were identified (1.04% prevalence). The most frequent antibodies were anti-M (19.4%), anti-E (19.0%), and anti-D (12.5%). Anti-D prevalence among D-negative mothers was 1.1%. Icelandic Medical Birth Registry data were available for 881 (96.6%) pregnancies. In the clinically significant group (n = 474), anti-E (27%) and anti-D (20%) were most common, whereas anti-M was most frequent (53%) in the clinically nonsignificant group (n = 407). Mothers in the clinically significant group were older, more often multigravidae, had more abortions and stillbirths, and had shorter gestational length. Newborns in the clinically significant group were less healthy, had lower weight and Apgar scores, and required more treatment. Among specificities in the clinically significant group, anti-D antibodies were most strongly associated with severe hemolysis. CONCLUSION: In this study, the prevalence of alloimmunization was similar to that in previous reports. Of all clinically significant antibodies, anti-D was most strongly associated with severe hemolysis, requiring phototherapy or exchange transfusions. Our data emphasize the importance of implementing an antenatal prophylactic RhIg program in Iceland in the near future.