Early diagnosis of ectopic pregnancy using receiver-operator characteristic curves of serum progesterone concentrations.

The objective was to assess the usefulness of serum progesterone concentrations in the differentiation of intra-uterine (viable and non-viable) and extra-uterine pregnancies. Progesterone concentrations were prospectively measured at 4, 5 and 6 weeks gestation in 338 pregnancies which resulted in 242 viable births, 81 abortions and 15 ectopic pregnancies. Progesterone threshold analysis was performed using receiver-operator characteristic curves. The progesterone threshold value for ectopic pregnancy at 4 weeks was 5 ng/ml, at 5 weeks 10 ng/ml and at 6 weeks 20 ng/ml. A significant difference was observed between all intra-uterine versus ectopic pregnancies (P = 0.0005), but not between viable versus non-viable intra-uterine pregnancies (P = 0.37). The differences were most clearly defined at 4 weeks and decreased with increasing gestation. We conclude that serum progesterone and gestational age taken together can differentiate intra-uterine from extra-uterine pregnancies with a very high sensitivity and specificity at 4 weeks gestation, a time when ectopic pregnancies are not evident on ultrasound examination.