Impact of Serum Progesterone Concentration on the Day of Embryo Transfer in Modified Natural Cycles and Stimulated Cycles on Ongoing Pregnancy Rate

Progesterone as a promoter of endometrial maturation is essential for the process of embryo implantation. The transformation of the endometrium from a proliferative state to a receptive state depends on the adequate progesterone exposure of the endometrium. Therefore, in any assisted reproduction technique (ART) the management of the luteal phase with exogenous administered progesterone, aiming to achieve a receptive endometrial state, is an essential part of the therapy. This important part of infertility-treatment is called luteal phase support (LPS).

Currently, there is a scientific debate and research regarding the timing, the dose and route of administration of exogenous progesterone in ART cycles. For years, the administration of progesterone was based on a "one fits all"- concept, mainly driven from the doctors and patients' preference regarding dose, timing and route of administration of the exogenous progesterone. Due to the lack of solid and evidence-based knowledge, the LPS improving investigating LPS is of outmost importance.

Therefore, improving the LPS is continuously in the focus of research and investigation. Main objectives of those efforts are to clarify the optimal timing, dosage and route of administration of progesterone for every possible ART procedure, in order to improve therapy outcomes. Of special interest in this wide field is the management of LPS in embryo-transfer-cycles such as substituted cycles and modified natural cycles for frozen-thawed cycles, and in fresh embryo-transfers after stimulated cycles.

Measuring serum progesterone levels in the luteal phase of a transfer cycle seems to be a promising approach in resolving the former mentioned doubts. Now, research focuses on luteal-phase serum progesterone levels as a predictor of outcomes. The discovery of certain thresholds of progesterone levels in the serum would give us a handy tool for individualizing the LPS with the main objective to improve outcomes.

Previous studies could show that there exist certain thresholds of serum progesterone in substituted cycles that could be used as a predictor. Furthermore, the same group could show that modifying the dose and the route of administration in the sense of individualizing LPS can improve outcomes.