Postpartum levels of circulating fetal microchimeric cells are lower after early-onset preeclampsia

Fetal cells may persist in the mother following pregnancy, termed fetal microchimerism. These cells have been attributed positive and negative effects. The number of fetal cells transferred during pregnancy appears to be higher in preeclampsia. Here, we investigate whether fetal cell presence and quantity in the maternal circulation 1-8 years postpartum is influenced by a previous preeclamptic pregnancy. We also relate fetal cells detected postpartum to fetal cells detected during pregnancy, time since index pregnancy, parity, fetal sex and maternal characteristics. A cohort of 139 women was included in the present study: 21 with previous early-onset preeclampsia, 31 with previous late-onset preeclampsia and 87 with a clinically uncomplicated index pregnancy. Circulating fetal microchimerism was detected in maternal buffy coat using qPCR, targeting alleles unique to the fetus. Pregnancy buffy coat samples were available for 129 of the 139 included women. Early-onset, but not late-onset, preeclampsia was associated with reduced quantity of fetal microchimeric cells in maternal circulation postpartum. Fetal cells detected during pregnancy, time since index pregnancy, parity, fetal sex and maternal characteristics were not predictive of microchimerism postpartum in our cohort. Our findings suggest that early-onset, but not late-onset preeclampsia, affects circulating microchimerism postpartum. Our observation that fetal microchimerism postpartum did not correlate with number of fetal cells detected during pregnancy nor time since index pregnancy supports the notion that fetal microchimerism is a dynamic phenomenon, with fetal cells moving in and out of maternal circulation and surrounding tissues, possibly affected by the current physiologic state of the mother.