Increasing quantity of maternal immunoglobulin G in trophoblastic tissue before the onset of normal labor.

While levels of maternal immunoglobulin G (IgG) increase in the fetal circulation during the third trimester, actual trophoblastic concentrations have not been extensively studied. To investigate this process, placentas from 71 patients with gestational ages between 26 and 42 weeks were examined by means of a peroxidase-antiperoxidase immunostaining technique specific for IgG. Linear regression revealed a significant increase in antibody with advancing gestational age (r = 0.36, p less than 0.01). In addition, placentas from patients in spontaneous term labor revealed a significantly higher antibody level when compared with those of patients at term delivered electively before the onset of labor (mean +/- SEM 2.6 +/- 0.2 vs 1.7 +/- 0.3, p less than 0.02). Patients in premature labor failed to demonstrate this increase in antibody staining. One possible explanation for these findings is an enhanced recognition of the fetal trophoblastic tissue by the maternal immune system at term. It also suggests immunologic factors may play an important role in the initiation of normal labor.