Circulating beta-2-microglobulin levels during pregnancy and their possible relationship with feto-maternal histocompatibility.

Plasma beta 2 microglobulin (beta 2m) levels have been measured by radioimmunoassay in normal pregnant women, in two successive pregnancies of a woman who shares HLA antigens with her husband, in normal twin pregnancies, in toxemic pregnancies and in hydatidiform moles. During normal pregnancy, plasma beta 2m levels decrease reaching a minimum at week 14 and increase thereafter to a maximum at week 34. In the two successive pregnancies of the one patient with HLA compatibility, beta 2m concentrations were significantly lower than in normal pregnancies. Women with monozygotic twins had significantly less beta 2m than women with heterozygotic twins. Toxemic patients bearing female fetuses had also statistically lower beta 2m levels than toxemic women with male fetuses. Patients suffering from hydatidiform moles had beta 2m levels in the range of normal pregnant patients. Since circulating beta 2m is produced by lymphocytes one might assume that low beta 2m levels reflect a reduced activity of lymphocytes. The results presented here allow to propose a hypothesis which will have to be verified that reduced beta 2m levels are associated with an increased feto-maternal histocompatibility.