TRANSPLACENTAL IGG SUBCLASS CONCENTRATIONS IN PREGNANCIES AT RISK OF HEMOLYTIC-DISEASE OF THE NEWBORN

The relationship of haemolytic disease of the newborn (HDN) to the tra nsplacental passage of the four IgG subclasses was assessed at varous gestational ages by comparing the maternal and fetal IgG subclass conc entrations in 34 pregnancies at risk of HDN with those in 30 pregnanci es not at risk. Higher maternal and fetal IgG1 levels were attained in pregnancies at risk of HDN than in pregnancies not at risk. In contra st, a slight decrease in maternal IgG2 and IgG4 levels occurred in pre gnancies at risk of HDN, as compared with a slight rise in maternal Ig G2 and IgG4 levels in pregnancies not at risk of HDN. Changes in fetal IgG2 and 4 concentrations in either type of pregnancy were very simil ar, showing only slight increases between the 19th and 34th week of ge station. A slight decrease in maternal IgG3 occurred in both types of pregnancy. In contrast, higher and fairly steady levels of fetal IgG3 were observed in fetuses not at risk of HDN throughout gestation, when compared with those in 'at risk' pregnancies. However, the statistica l reliability of these results is not clear since only small numbers o f samples were tested and because wide variations in IgG concentration s were observed. The IgG subclass concentrations in 50 paired maternal and cord blood samples were also measured and revealed that IgG1 leve ls were substantially higher in cord rather than maternal blood; cord and maternal IgG2, 3 and 4 levels, on the other hand, were fairly simi lar.