Combined use of progesterone and human chorionic gonadotropin determinations for differential diagnosis of very early pregnancy.

Progesterone (P) level and daily change in human chorionic gonadotropin (hCG) were determined in the serum of 307 patients with suspected ectopic pregnancy (EP). Of the viable intrauterine pregnancies (IUP), 99% had P values above 30 nmol/L, whereas 75% of the EP and 81% of the spontaneous abortions had P values less than 30 nmol/L. Among the viable IUP, 95% had normal hCG increases, whereas 89% of the EP and 99% of the spontaneous abortions had abnormal hCG increases. A P value less than 30 nmol/L combined with an abnormal hCG increase had a positive predictive value for pathological pregnancy of 1.0. Consequently, in such cases, further invasive diagnostic or therapeutic measures can be taken with a low risk of jeopardizing a viable IUP.