Received October 17, 2021
Accepted March 20, 2022

Objetive: To assess the association between serum level of progesterone during stimulation and in the luteal phase with pregnancy rate in a cohort of patients undergoing in vitro fertilization and embryo transfer (IVF-ET) on day 5. Methods: Retrospective Cohort Study. Patients: 62 infertile women, aged 24-42 years, undergoing in ART at our center, from May 2019 to May 2021. Progesterone was evaluated during ovarian stimulation day 2, day 6, day 8 of stimulation, day of trigger (P4dhCG) and on the day of blastocyst transfer with 5 days of progesterone supplementation (P4d5+). We also realized the difference of P4d5+ with P4dhCG. (ΔP4). After, we divided the patients into two groups based on the serum level of progesterone at P4d5+; < 10ng/ml (Group A), ≥10ng/ml (Group B). The Student’s t-test was performed for continuous variables; Mann- Whitney´s Test and Spearman´s Test were used where appropriate for categorical variables. p< 0.05 was considered statistically significant. Results: There were a positive correlation between βhCG positive with P4d5+ (p<0,001; Rho 0.770) and with ΔP4 (p<0,001; Rho 0.703). The serum progesterone level on the fifth day of progesterone supplementation when ≥ 10ng/ml, the pregnancy rate was double that when P4<10ng/ml (44% x 21%, respectively). Conclusions: The pregnancy rate was positively correlated with the serum P4 level on the fifth day of progesterone supplementation, and with the difference between the serum progesterone level in the Dd5+ / dhCG. The serum progesterone level on the fifth day of progesterone supplementation when ≥ 10ng/ml had higher pregnancy rate.