Fetal vasopressin in late pregnancy. Levels in amniotic fluid and in fetal urine.

The concentrations of vasopressin in the amniotic fluid were measured in 40 patients. The pregnancies were complicated by diabetes, toxemia or imminent premature delivery and in one case by polyhydramnion. The gestation time varied from 33 to 41 weeks. In addition, we measured vasopressin concentrations after transabdominal drainage of fetal bladder in three cases with urethral obstruction. Detectable concentrations of vasopressin in the amniotic fluid were found in all but four of the 40 cases observed. The vasopressin concentrations varied from 0.21 to 1.81 pg/ml. There were no systematic differences in the values in relation to duration of gestation or disease present. The highest vasopressin concentration was observed in the patient with polyhydramnion. No detectable amount of vasopressin was found in the urine of the three fetuses examined. The results suggest that, in contrast to earlier studies, the placenta may be permeable to small amounts of vasopressin or may itself be an origin of this hormone. The maternal complications present seem to have no effect of the vasopressin concentrations in the amniotic fluid.