Delayed blastocyst development is influenced by the level of progesterone on the day of trigger.

PURPOSE: To evaluate the association between progesterone (P) level on the day of trigger and time to blastulation in IVF cycles. METHODS: This was a retrospective cohort study with autologous IVF cycles performed at our Institution from January 2019 to December 2021. A total of 1109 IVF cycles were included. The primary outcome was to compare time to blastulation in terms of percentage of expanded (grade 3) blastocysts on day 5 according to progesterone level at trigger. RESULTS: A total of 3517 blastocysts were analyzed. After dividing progesterone level in quartiles (Q1, P < 0.50 ng/ml; Q2 0.50 ng/ml ≤ P ≤ 0.78 ng/ml; Q3, 0.79 ng/ml ≤ P ≤ 1.15 ng/ml; Q4, P > 1.15 ng/ml), we observed a delay in blastocyst development according to the increasing level of progesterone at trigger (analysis by rank, P-value = 0.01). After adjusting for confounding factors at the multivariate analysis, the percentage of day 5 blastocysts was reduced for Q3 (- 13.8%, 95% CI from - 20.5 to - 7.0%, p < 0.001) and Q4 (- 7.7%, 95% CI from - 15.5 to 0.0%, p = 0.05) compared to Q1 (reference). CONCLUSIONS: Progesterone levels on day of trigger correlate to the percentage of expanded (grade 3) blastocysts on day 5 and a delayed blastocyst development day 5 is expected for high progesterone levels.