Endocrinology of in-vitro fertilization pregnancies during the first trimester

The endocrine function of the corpus luteum and placenta andthe inter-relationships between ovarian steroids and the placentalproteins in pregnancies achieved following ovarian stimulation,in-vitro fertilization and embryo transfer (IVF-ET) have beeninvestigated. The serum concentrations of human chorionic gonadotrophin(HCG), Schwangerschaft protein-1 (SP-1), pregnancy-associatedplasma protein A (PAPP-A), progesterone and oestradiol weremeasured at weekly intervals between the 4th (ET plus 2 weeks)and 14th week of gestation in 86 pregnancies. The mean concentrationsof the placental proteins and oestradiol were significantlyhigher in twin than in singleton pregnancies from as early as5 weeks gestation, but the mean concentrations of progesteronewere significantly higher only at the end of the first trimester.Ranking, as demonstrated by the presence of statistically significantcorrelations between serum levels of each substance analysedin week 13 with those of preceding weeks, was established forprogesterone and SP-1 from the 5th week, for oestradiol andPAPP-A from the 7th week and for HCG from the 8th week of gestation.The presence of statistically significant correlations betweeneach substance analysed suggests that the placenta becomes thedominant source of oestradiol from 8 weeks gestation and ofprogesterone not until 12 weeks gestation, and that the placentalsynthesis of HCG, SP-1, PAPP-A, oestradiol and progesteroneappear to be linked. There were no statistically significantcorrelations between the serum concentrations of HCG and eitherprogesterone or oestradiol until the production of each hadbecome predominantly placental.