Fetal blood mononuclear cell division in normal and pathological pregnancies

Fetal blood mononuclear cell division was measured using flow cytometry in 53 normal pregnancies and 51 pathological pregnancies complicated either by anaemia due to red blood cell isoimmunisation (RCI: n = 21), intrauterine growth retardation (SGA: n = 13) or abnormal karyotype (n = 17). In normal pregnancy, mononuclear cell division rates decreased with gestational age from a mean of 1.8% at 18 weeks to 1% at 40 weeks. Furthermore, there was a significant association between cell division and erythroblast count. The rates of cell division and erythroblast count were significantly increased in the chromosomally abnormal fetuses, and significantly decreased in the transfused RCI fetuses compared to the controls. Although the erythroblast count was elevated in the SGA fetuses, the mononuclear cell division was not significantly different from the controls. Fetal blood mononuclear cell division is elevated in early pregnancy and in chromosomally abnormal fetuses, probably as a consequence of increased numbers of circulating haemopoietic precursors. Mononuclear cell division is decreased in transfused RCI fetuses as a consequence of suppressed erythropoiesis. In SGA fetuses, despite the increased erythropoietic stimulation and erythroblastosis, cell division is not increased.