Pregnancy: Corpus luteum failure in ectopic pregnancy

The endocrinology of ectopic pregnancy was studied in orderto investigate the origin of the discordance in the circulatingamounts of human chorionic gonadotrophin (HCG) and those ofoestradiol and progesterone. Serial maternal blood samples wereobtained at 4–9 weeks gestation from 93 patients who becamepregnant following in-vitro fertilization and embryo transferincluding 10 ectopic, 21 anembryonic and 62 normal singletonpregnancies. The samples were analysed for HCG, Schwangerschaftprotein-1 (SP-1), pregnancy-associated plasma protein-A (PAPP-A),progesterone and oestradiol. In ectopic pregnancies, concentrationsof all substances analysed were significantly reduced comparedto singleton pregnancies from 5 weeks gestation (P < 0.05–0.001)but they were not significantly different from those of anembryonicpregnancies. In ectopic pregnancies, associations were foundbetween the concentration of both HCG and SP-1 and those ofprogesterone and oestradiol. No associations were found betweenPAPP-A and any other substances analysed. This may be due toinsensitivity of the PAPP-A assay; alternatively PAPP-A concentrationsmay be differentially reduced in ectopic pregnancy. These findingssuggest that progesterone and oestradiol are derived from thecorpus luteum in early ectopic pregnancy but that the corpusluteum fails rapidly and the dominant source of both hormonesbecomes the trophoblast as early as 5 weeks.