Factors associated with the acquisition and retention of male-origin microchimerism in women

Natural microchimerism is the presence of cells at low concentrations in one individual originating from another. Although most cells are cleared from the maternal vascular system shortly after delivery, microchimeric cells - presumably of fetal origin - can be detected in many women decades after pregnancy.

This cross-sectional study includes 774 women who participated in the Danish Diet, Cancer, and Health cohort sampled from 1993 to 1997. We investigate sources of male-origin microchimerism related to childbearing in maternal peripheral blood and its association with lifestyle using logistic regression. Guided by previous reports, we distinguish between sources of acquisition and retention of male-origin microchimerism.

Women who had given birth to a male fetus had significantly increased odds of testing positive for male-origin microchimerism compared with women who had never given birth to a male fetus (OR = 1.61, 95 % CI [1.12; 2.33]). Compared with current users of hormone replacement treatment, women who reported no or former use of hormone replacement treatment had increased odds of testing positive for male-origin microchimerism (OR = 1.57, 95 % CI [1.12; 2.21]; OR = 1.89, 95 % CI [1.14; 3.13]). Furthermore, women who reported having formerly smoked had increased odds of testing positive for male-origin microchimerism, compared with women who reported current smoking (OR = 1.77, 95 % CI [1.15; 2.75]).

We find that the acquisition of male-origin microchimerism is associated with pregnancy with a male fetus, and retention may be linked to external factors, including smoking.