IVF and the exogenous progesterone-free luteal phase

Luteal phase support in assisted reproductive technology

Infertility affects one in six couples, with in vitro fertilization (IVF) offering many the chance of conception. Compared to the solitary oocyte produced during the natural menstrual cycle, the supraphysiological ovarian stimulation needed to produce multiple oocytes during IVF results in a dysfunctional luteal phase that can be insufficient to support implantation and maintain pregnancy. Consequently, hormonal supplementation with luteal phase support, principally exogenous progesterone, is used to optimize pregnancy rates; however, luteal phase support remains largely 'black-box' with insufficient clarity regarding the optimal timing, dosing, route and duration of treatment. Herein, we review the evidence on luteal phase support and highlight remaining uncertainties and future research directions. Specifically, we outline the physiological luteal phase, which is regulated by progesterone from the corpus luteum, and evaluate how it is altered by the supraphysiological ovarian stimulation used during IVF. Additionally, we describe the effects of the hormonal triggers used to mature oocytes on the degree of luteal phase support required. We explain the histological transformation of the endometrium during the luteal phase and evaluate markers of endometrial receptivity that attempt to identify the 'window of implantation'. We also cover progesterone receptor signalling, circulating progesterone levels associated with implantation, and the pharmacokinetics of available progesterone formulations to inform the design of luteal phase support regimens.

GnRHa trigger-the story of the ugly duckling

The objective of this invited review is to describe the introduction and development of the GnRH agonist (GnRHa) trigger protocol in modern in vitro fertilization, focusing on ovarian hyperstimulation syndrome (OHSS) prevention and, equally important on the role of GnRHa trigger as an opener of the luteal phase "black box." The GnRHa trigger and freezing of all embryos is the ultimate weapon against OHSS in the OHSS-risk patient. In the non OHSS-risk patient, GnRHa trigger followed by a modified luteal phase support with lutein hormone activity and subsequent fresh embryo transfer results in excellent reproductive outcomes. Thus, the GnRHa trigger has paved the way for a virtually OHSS-free clinic, and equally important is the fact that the early lessons learned from studying the GnRHa trigger opened the "black box" of the luteal phase enabling improved reproductive outcomes in both fresh and frozen embryo transfer cycles.