Endocrinology in luteal phase and implantation

The normality of the luteal phase after superovulation depends on the method and adequacy of the stimulation regimen. In comparison with natural cycles, the luteinisation of multiple follicles produces higher concentrations of steroids in blood, and soon after ovulation a correct ratio of serum oestradiol (E2) to progesterone is critical to establish viable pregnancies. Out of phase and asynchronous endometria can arise after stimulation with clomiphene (CC) alone or in association with human menopausal gonadotrophin (HMG), and pregnancies mostly arose in patients with advanced endometrial characteristics and elevated post-ovulatory levels of serum progesterone after HMG stimulation. Increasing plasma progesterone concentrations in the early luteal phase with natural progesterone can thus be considered as a rational approach to improve rates of implantation. Premature luteal regression is frequently observed after HMG stimulation whether or not in association with gonadotrophin releasing-hormone agonists (GnRHa). Support to the theca lutein cells is mandatory before sufficient human chorionic gonadotrophin (HCG) is produced by the embryo. Deficient luteal phases can be treated with hormonal support, but the efficacy of routine luteal supplementation after ovarian hyperstimulation has still to be proven in larger controlled trials.