Sex, male origin microchimerism, and mortality in a Danish cohort

We previously demonstrated that women with detectable male cells in peripheral blood – male origin microchimerism (a presumed souvenir from pregnancy) – enjoy half the risk of all-cause mortality compared with women tested negative. However, such differences are vulnerable to confounding. Also, it is unknown whether better survival in women vs. men is confined to women testing male origin microchimerism positive. In this updated analysis, we first compared the survival of positive and negative women using prognostic score weighing to minimize potential confounding. Next, we compared the survival of women tested positive and negative for male origin microchimerism to men. Women (n = 766) and men (n = 1,000) from the Diet, Cancer, and Health cohort aged 50–64 years in 1993–1997 were followed until 2017 for all-cause mortality in national Danish registers. Based on predictors of death, we calculated prognostic scores for all women and compared mortality according to male origin microchimerism status by prognostic score weighted Cox regression adjusting for potential confounding. Next, we compared mortality across positive/negative women and men. Women who tested male origin microchimerism positive versus negative had a 50% lower mortality rate (adjusted HR = 0.50 [95% CI 0.32–0.77]). Compared with men, women who tested positive had a 51% lower mortality rate (HR = 0.49 [95% confidence interval (CI) 0.38–0.61]), whereas women who tested negative had a similar rate (HR = 0.83 [95% CI 0.63–1.09]). Women who tested positive for male origin microchimerism lived longer than their counterparts who tested negative, who appeared to have a similar survival pattern to that of men.