Accumulation of colony-stimulating factor 1 in amniotic fluid during human pregnancy.

Colony-stimulating factor 1 is a hematopoietic growth factor that increases 1000-fold in the uteri of pregnant mice, and its receptor is abundantly expressed in the human placenta. The concentration of colony-stimulating factor 1 in amniotic fluid at 33 to 40 weeks (9.0 +/- 1.1 ng/ml) was twofold higher than that at 16 to 18 weeks gestation (4.1 +/- 0.5 ng/ml), whereas maternal serum colony-stimulating factor 1 levels did not rise significantly. Colony-stimulating factor 1 was detected in endometrial extracts from pregnant women and levels were higher than those in extracts from nonpregnant women.