Circulating maternal serum progesterone in high-risk pregnancies.

Serum progesterone was measured by competitive protein-binding assay in 331 cases of normal pregnancy ranging from 6 to 42 weeks. Serial estimations of serum progesterone were performed in nine cases of severe hypertensive disorder of pregnancy, eight cases of twin pregnancy, three cases of twin pregnancy complicated by severe hypertensive disorder of pregnancy, three cases of triplet pregnancy, three cases of previous bad obstetric history, one case of anencephaly, and seven cases of intrauterine fetal death. Serum progesterone remained within normal range in severe hypertensive disorder of pregnancy and the levels were indistinguishable in cases of fetal growth retardation from those without growth retardation. In twin and triplet pregnancies, serum progesterone was within normal range or elevated and was usually higher than normal in twin pregnancies after weeks 33 to 34. Serum progesterone levels were normal in anencephalic pregnancy and in most cases of intrauterine fetal death. The findings are discussed with reference to placental hormonal activity. It is concluded that serum progesterone is a poor index of placental function.