High serum human macrophage colony-stimulating factor level during pregnancy.

Using a specific enzyme immunoassay, we monitored the serum levels of human macrophage colony-stimulating factor (hM-CSF) in pregnant women during gestation and after delivery. During pregnancy there was a marked elevation of maternal serum hM-CSF level, which returned to the baseline level within 3 weeks after delivery. The changes in maternal serum hM-CSF level were associated with changes in the numbers of monocytes and neutrophils in the maternal peripheral blood. Fetal sera prepared from cord blood samples also had a high hM-CSF level. In contrast to the baseline level of hM-CSF in maternal sera after delivery, the hM-CSF levels of newborn infants at 1 to 7 days after birth were higher than fetal levels, indicating that fetuses and newborn infants are a source of hM-CSF. The serum hM-CSF levels of infants at 22 to 35 days were between fetal levels and normal adult levels. Human M-CSF found in the serum of pregnant women and in cord blood was predominantly the large form of M-CSF, with a molecular mass of 85 kDa. Human M-CSF levels in amniotic fluid at 30 to 40 weeks were higher than those in cord blood sera at the same stage, indicating that the uterus is another source of hM-CSF. The roles played by hM-CSF during pregnancy need to be investigated.