LAUSR

To assess the impact of serum progesterone level and the progesterone/estradiol ratio on determining the appropriate day of embryo transfer in fresh IVF/ICSI cycles without premature progesterone elevation. This was a retrospective cohort study in a university teaching hospital. Only fresh embryo transfer cycles in the GnRH-antagonist protocol without elevated trigger-day progesterone levels (n = 508) were analyzed after taking into consideration the exclusion criteria. The main outcome measure was to determine the association between below and above of the cut-off values of serum progesterone level and P/E2 ratio regarding clinical pregnancy, ongoing pregnancy and live birth rates. These rates were assessed with the use of percentile and logistic regression analyses according to the threshold levels of serum progesterone levels < 0.85 ng/mL versus ≥ 0.85 ng/mL on the day of hCG administration. The clinical pregnancy rates were significantly lower in fresh cycles with P levels ≥ 0.85 ng/mL on the day of hCG administration than in cycles with P levels < 0.85 ng/mL for the cleavage-stage embryo transfers (26.7% vs. 47.5%, p = 0.001). Blastocyst-stage embryo transfer improved pregnancy results although the P levels were ≥ 0.85 ng/mL (53.8% vs. 51.4%, p > 0.05). The adjusted odds ratio of P levels < 0.85 ng/mL revealed significant differences in only cleavage-stage embryo transfer cycles (aOR = 0.424, p = 0.016). Although serum progesterone levels are below the accepted cut-off level of 1.5 ng/mL, there may be reduced pregnancy outcomes in fresh embryo transfer cycles. A threshold level such as 0.85 ng/mL may ensure the decision to replace the cleavage stage with the blastocyst-stage embryo transfer in fresh cycles without premature progesterone elevation.