Endocrinology of in-vitro fertilization pregnancies during the first trimester.

The endocrine function of the corpus luteum and placenta and the inter-relationships between ovarian steroids and the placental proteins in pregnancies achieved following ovarian stimulation, in-vitro fertilization and embryo transfer (IVF-ET) have been investigated. The serum concentrations of human chorionic gonadotrophin (HCG), Schwangerschaft protein-1 (SP-1), pregnancy-associated plasma protein A (PAPP-A), progesterone and oestradiol were measured at weekly intervals between the 4th (ET plus 2 weeks) and 14th week of gestation in 86 pregnancies. The mean concentrations of the placental proteins and oestradiol were significantly higher in twin than in singleton pregnancies from as early as 5 weeks gestation, but the mean concentrations of progesterone were significantly higher only at the end of the first trimester. Ranking, as demonstrated by the presence of statistically significant correlations between serum levels of each substance analysed in week 13 with those of preceding weeks, was established for progesterone and SP-1 from the 5th week, for oestradiol and PAPP-A from the 7th week and for HCG from the 8th week of gestation. The presence of statistically significant correlations between each substance analysed suggests that the placenta becomes the dominant source of oestradiol from 8 weeks gestation and of progesterone not until 12 weeks gestation, and that the placental synthesis of HCG, SP-1, PAPP-A, oestradiol and progesterone appear to be linked. There were no statistically significant correlations between the serum concentrations of HCG and either progesterone or oestradiol until the production of each had become predominantly placental.