Because the cause of the majority of recurrent pregnancy losses is unknown, it has been suggested that some may be due to alloimmune causes. It has been speculated that HLA compatibility of the couple, absence of maternal leukocytotoxic antibodies, or the absence of maternal blocking antibodies may be responsible. All of these have been investigated and treatment directed toward these abnormalities has been studied. Mowbray, et al performed a double-blind trial of treatment with husband's purified lymphocytes in 1985, and the results suggested improvement in pregnancy outcome. A more recent multicenter study by Ober, et al showed, in a much larger group of patients, that paternal lymphocyte immunization resulted in no beneficial effect.
Others have shown that increased levels of natural killer (NK) cells are present in women with chromosomally normal miscarriages and that increased levels of NK cells are present in non-pregnant women with a higher chance of SAB in a subsequent pregnancy. In contrast, more recent studies have shown no relationship between the risk of pregnancy loss and the presence or absence of HLA compatibility, leukocytotoxic antibodies, blocking antibodies, or elevated NK cell activity. At this point, the role of alloimmunity in the mechanism of recurrent pregnancy loss is unclear, so the treatment of these problems is still speculative and investigational.
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