Plasma Progesterone Levels in Normal and Abnormal Early Human Pregnancy

Abstract

Plasma progesterone levels were measured by a competitive protein-binding method (Radwanska E, Swyer GIM: J Obstet Gynaecol Br Commonw 81:107, 1974) in 224 women during the first trimester of pregnancy—127 in normal pregnancy, 66 hospitalized with symptoms of threatened abortion, 10 with missed abortion, 11 with ectopic pregnancy, and 10 with incomplete abortion. In normal early pregnancy (6 to 12 weeks), plasma progesterone levels ranged from 10 to 54 ng/ml (mean ± standard deviation: 25.5 ± 10.3 ng/ml; n = 158). In cases of threatened abortion between 6 and 12 weeks in which pregnancy progressed successfully to term, the first-trimester plasma progesterone levels ranged from 5 to 42 ng/ml (22.5 ± 9.2 ng/ml; n = 25)—not significantly different from normal pregnancies. In women with threatened abortion who subsequently aborted, they ranged from 3 to 48 ng/ml (14.1 ± 9.9 ng/ml; n = 77)—significantly lower (P < 0.001) than the mean for normal pregnancies and for those patients with threatened abortion whose pregnancies continued. In cases of missed abortion, the plasma progesterone level ranged from 3 to 12 ng/ml (7.0 ± 2.0 ng/ml; n = 18), suggestive of defective pregnancy. In all 10 cases admitted to the hospital with incomplete abortions the plasma progesterone level was below 2 ng/ml, confirming the clinical findings. The diagnosis of early pregnancy abnormalities, especially in clinically more difficult cases, was greatly facilitated by the use of plasma progesterone estimation, a low progesterone level usually indicating nonviable pregnancy.