The prevalence of recurrent fetal loss and its relationship to sharing of human leukocyte antigens within couples was examined in a large, ethnically homogeneous Chinese population in Taiwan: 91 couples with primary recurrent spontaneous abortion, 32 couples with secondary recurrent spontaneous abortion, and 51 normal fertile couples. There was an excess of human leukocyte antigen sharing in both types of recurrent aborters. The primary aborters shared human leukocyte A and DO antigens and three or more of the human leukocyte A, B, DR, and DO antigens. The secondary aborters did not have an excess of sharing at any one locus but they did share three or more of the human leukocyte A, B, DR, and DO antigens. There was no excess of antipaternal cytotoxic antibodies in any group of aborters, and the primary aborters had a lower level of mixed lymphocyte reaction blocking factor than normal couples or secondary aborters. Previous studies showed that couples in whom a gestational trophoblastic tumor developed in the woman shared human leukocyte B and DO antigens and three or more of the human leukocyte A, B, DR, and DO antigens. These studies provide substantial support for the role of recessive genes linked to the major histocompatibility complex in the pathogenesis of recurrent spontaneous abortions and of gestational trophoblastic tumors.
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