Placental transport of maternal immunoglobulin G in pregnancies at risk of Rh (D) hemolytic disease of the newborn.

PROBLEM: The following questions were addressed: Is the placental transport of immunoglobulin (Ig)G, IgG1, and IgG3 diminished in pregnancies at risk of hemolytic disease of the newborn? Is the placental transport of IgG, IgG1, and IgG3 correlated with the hemoglobin concentration in the fetus and AutoAnalyzer (AA) quantitations of maternal anti-D?

METHOD OF STUDY: IgG concentrations were determined retrospectively in 41 paired fetal/maternal (f/m) samples in 31 Rh (D) alloimmunized pregnancies. IgG1 and IgG3 concentrations were determined in those 23 cases in which the results of fetal hemoglobin concentration and quantitations of maternal anti-D were available. The results were compared with values found in normal pregnancy and correlated with maternal anti-D AA quantitations and fetal hemoglobin concentrations.

RESULTS

Fetal IgG, IgG1, and IgG3 concentrations, and the corresponding fetomaternal ratios in Rh (D) alloimmunized pregnancies, increased with gestational age according to the following formulas (obtained by simple regression): Fetal IgG = -8.846 + 0.491.gestational age (GA), (R2 = 0.544); fetal IgG = 10.021 + 0.46.GA (R2 = 0.463); fetal IgG3 = -0.865 + 0.039.GA, (R2 = 0.327); f/m IgG = -1.006 + 0.054.GA, (R2 = 0.557); f/m IgG1 = -1.876 + 0.085.GA, (R2 = 0.654); f/m IgG3 = -0.199 + 0.026.GA, (R2 = 0.146).

CONCLUSIONS

The placental transport of IgG, IgG1, and IgG3 in women with Rh (D) immunizations is not diminished compared with normal pregnancy. However, AA quantitations of anti-D are inversely correlated with f/m IgG ratio, f/m IgG1 ratio, and fetal IgG and IgG1 concentrations (P = 0.002, P = 0.004, P = 0.02, and P = 0.02 respectively). The placental transport of IgG3 is significantly higher in pregnancies at risk of hemolytic disease of the newborn compared with IgG3 concentrations in normal pregnancy.