| Abstract
| - The objective was to assess the usefulness of serum progesterone concentrations in the differentiation of intrauterine (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.
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