#381 : Can Serum Progesterone Concentration Direct a Fresh or Freeze-All Transfer Strategy in the First In Vitro Fertilisation Cycle?

Background and Aims: The role of progesterone in preparing the endometrium for implantation and sustaining early pregnancy is well established in ART, however the role of serum progesterone measurement within cycles in determining the outcome of embryo transfer (ET) is not defined. This study aimed to examine the interaction between serum progesterone concentration on the day of HCG trigger and choice of freeze-all and fresh transfer strategies on live birth. Method: We retrospectively studied 26661 women (Chengdu Xinan Hospital) commencing their first IVF cycle using autologous gametes between January 2015 and September 2019. We excluded cycles where oocyte retrieval was cancelled or no embryos were available for transfer, cycles where fresh or frozen transfer was determined by patient preference, and when serum progesterone on day of HCG was [Formula: see text] 2.0 or [Formula: see text] 20 oocytes were collected. The primary outcome of interest was live birth after 28 weeks gestation following first ET and expressed as an odds ratio (OR). Results: The predicted odds of live birth were greater in the frozen ET group at all progesterone concentrations. The effect was more pronounced with progressive increase in progesterone concentration (Figure 1) and maintained in both unadjusted and adjusted models. For women >35 years (n=4687), a positive interaction between progesterone and treatment effect was present although the treatment effect curve was flattened (p for interaction = 0.01). Conclusion: In an unselected population undergoing IVF/ICSI, there is an increased chance of pregnancy with a freeze all ET strategy at different progesterone concentrations on HCG trigger day. The effect appears to be dose related with increasing magnitude of effect with rising progesterone concentration. This interaction was also observed in subsets of women with single ET and women > 35 years old, however the benefit of a freeze-all policy appears low in these women.