Objective: The objective of this study was to quantitatively determine an immunoglobulin G receptor, placental alkaline phosphatase, and its ligand immunoglobulin G in maternal and fetal blood and to study the transport capacity of the receptor.
Study design: Venous blood samples from 66 term pregnant women and cord samples from their fetuses were obtained, together with the corresponding placentas.
Results: Mean placental alkaline phosphatase levels were determined to be 23.7 ng/ml and 1.2 ng/ml in maternal and fetal blood, respectively. Mean immunoglobulin G level of the fetal samples was significantly higher than that of the maternal samples (12.6 vs 9.5 gm/L, p < 0.0001). The placental alkaline phosphatase phenotype S had a larger dissociation constant to immunoglobulin G than did type F and was found to have mean fetal immunoglobulin G levels higher than those of the F type (13.3 vs 9.7 gm/L).
Conclusion: The placental immunoglobulin G receptor placental alkaline phosphatase is found in the fetal circulation. The placental alkaline phosphatase phenotype was found to be related to the levels of its ligand immunoglobulin G in fetal blood, although the mechanism for this remains to be established. Immunoglobulin G is actively transported to fetal blood to reach higher levels than in the maternal circulation.