Lewis phenotype of erythrocytes and Leb-active glycolipid in serum of pregnant women.

In an attempt to provide an explanation for the previously reported effect of pregnancy on the Lewis phenotype of erythrocytes, the level of Leb-active glycolipid in serum was compared with the reactions of erythrocytes, using samples obtained from 73 nonpregnant women, 74 women at the time of delivery, and 2 women at weekly intervals during their pregnancy. In this Swedish population, the frequency of the Le(a--b-) blood group increased from 11% in nonpregnant women to 36% in women at the time of delivery. Among Le(a--b+) women of all ABO groups, those who were A1 most often became (Leb-) during pregnancy. The change in phenotype occurred as early as the 24th week of gestation; the Leb antigen was again detectable within 6 weeks after delivery. The concentration of Leb glycolipid in serum, as measured by radioimmunoassay, decreased only slightly during pregnancy. The repartition of glycolipids, secondary to the increased ratio of lipoprotein to red cell mass that occurs during pregnancy, may account for the relative lack of Lewis glycolipid on erythrocytes.