Immunological and microbiological studies of midtrimester amniotic fluid.

Midtrimester amniotic fluids (MAF) from 73 women undergoing an amniocentesis were studied. The mean immunoglobin G (IgG) level was 34 +/- 14 mg/dl, which is higher than that reported in the third trimester. The maternal serum:MAF IgG ratio was 29 suggesting the blood:MAF barrier is less restrictive than others like the blood:cerebrospinal fluid barrier. Antibodies to herpes simplex virus (HSV) type 1 were detected in 78% of the MAF and the maternal serum:MAF HSV antibody titer ratio was 33. Antibodies to cytomegalovirus (CMV) were found in 84% of the MAF and the maternal serum:MAF CMV antibody titer ration was 40. Whenever either antibody was detected in the maternal serum it was also found in the MAF. No viruses, bacteria, mycoplasma, fungi and chlamyidae were isolated from MAF.