Absence of a factor blocking a cellular cytotoxicity reaction in the serum of women with recurrent abortions.

The serum of pregnant women contains a non-specific immunosuppressive factor able to block an in vitro cellular cytotoxicity reaction. This activity increases during the first trimester and persists for 3 months after delivery. The factor is active in dilution. Ten women who had recurrent abortions were typed for HLA antigens and were found to share several antigens with their husband. In all these women, the 'blocking factor' was absent from their serum. The absence of the 'blocking factor' could be used as a clinical test to predict spontaneous abortion.