Is luteal function maintained by factors other than chorionic gonadotrophin in early pregnancy?

Women with ectopic pregnancy (n = 14) and early embryonic arrest ('blighted ovum') (n = 9) were studied 16 days after conception, at a time when they were asymptomatic and serum concentrations of beta-human chorionic gonadotrophin (HCG) were in the normal range and increasing at an apparently normal rate. Serum progesterone and oestradiol concentrations were compared with those from normal women matched for gestational age and serum beta-HCG concentration whose singleton intra-uterine pregnancies proceeded normally beyond 20 weeks. Mean serum progesterone concentrations were significantly lower in the women with ectopic pregnancies than in matched controls (P < 0.002); however, there was no difference in the serum progesterone concentrations between women with blighted ova and matched controls. Statistically significant differences were not seen in serum oestradiol concentrations between either group and matched controls. Similarly there was no difference in serum progesterone or oestradiol concentrations in 20 women who conceived ectopic pregnancies and 20 women conceiving blighted ovum pregnancies and their matched intra-uterine controls when conception followed ovarian stimulation. The low serum progesterone concentrations seen in ectopic pregnancy suggest that there is a specific and selective deficiency in progesterone synthesis, which implies that factors other than HCG may influence luteal function.