Red cell alloimmunization during pregnancy

Sammanfattning: We have evaluated a new screening program to detect red cell alloimmunization during pregnancy that was introduced in the south-east region of Sweden in 1981. The screening program is based on two antibody tests at 25 and 35 gestational weeks for all pregnant  women regardless of maternal Rh(D) status. During the period 1983-89, all pregnant women in the region were tested (78,300) and 0.37% were found to exhibit red cell alloimmunization. Antibodies with anti-D specificity were the most common (34%), followed hy anti-E (24%), anti-Kell (17%) and anti-c (11%). These immunizations also caused the most severe cases of hemolytic disease of the newborns. The screening program was efficient since no newborn subjected to exchange transfusion was overlooked. Most of the new immunizations occurred among the Rh(D) positive women (63%). However, the cost of detecting a few severely affected fetuses among the Rh(D) positive women is high. In this group of pregnancies, it seems sufficient with only one antibody screening test, if done at 25 gestational weeks.The standard variables commonly used to predict fetal hemolytic disease (FHD) were studied. A low antibody titer level in maternal sernm (≤32) accurately predicted unaffected fetuses. When moderately elevated antibody titer levels (≥64) were present, complementary test variables were needed for a relaihle prediction of FHD. In Rh(D) alloimmunizations, the anti-D concentration in maternal serum, with a cut-off level of 0.7 µg/mL, was the best complementary variable. We could accurately distinguish a low-risk group from a high-risk group of pregnancies. Measurement of the bilirubin content in aruniotic fluid (ΔOD450) did not give any further information of relevance in predicting PHD.High-dose intravenous immunoglobulin (IVIG) treatment appeared to prevent a further deterioration of PHD when a moderate to severe FHD was present (B-hemoglobin concentration between 70-100 g/L). This was observed as a stabilized fetal hemoglobin concentration and an increased fetal anti-D concentration, both interpreted as an effect of a decreased erythrophagocytosis in the fetal reticuloendothelial system.We propose a flowchart with guidelines for the management of pregnancies complicated by red cell alloimmunization.