Detectability and pattern of immunoglobulins in normal amniotic fluid throughout gestation.

Immunoglobulin (Ig) M, IgA, and IgD class and IgA, and IgA2 subclass levels were detected in normal amniotic fluid throughout gestation with a hemagglutination-inhibition assay: IgG was measured by single radial immunodiffusion. In 161 tested samples, IgA, IgA, IgA2, and IgG were measurable in all cases; IgM was measurable in 99.4 per cent and IgD, in 90.6 per cent of the fluids. IgA, IgG, and IgD concentrations increased toward midpregnancy and thereafter decreased to term in a pattern similar to that for amniotic fluid total protein. IgM, on the other hand, remained relatively constant through week 35 of gestation; thereafter, it increased to term. There was no correlation in this normal group between amniotic fluid and cord blood levels of Ig class or subclass at term. Mean IgA values were 2.2 times higher in amniotic fluid than in cord serum. This was in sharp contrast to IgM, which was 16 times higher, IgG, which was 66 times higher, and IgD, which was 2.4 times higher in cord serum than in amniotic fluid. The inverse data for IgA as compared to other Ig classes suggest that amniotic fluid IgA may be partially derived from IgA in fetal gastrointestinal and pulmonary secretions. Determination of the concentration of the different Ig classes (and eventually subclasses) in amniotic fluid may be useful in diagnosis of intrauterine infections, malformations, and immunodeficiencies.