Low serum progesterone on the day of embryo transfer is associated with a diminished ongoing pregnancy rate in oocyte donation cycles after artificial endometrial preparation: a prospective study

STUDY QUESTION: Is there a relationship between serum progesterone (P) and endometrial volume on the day of embryo transfer (ET) with ongoing pregnancy rate (OPR) in artificial endometrium preparation cycles? SUMMARY ANSWER: Patients with serum P < 9.2 ng/ml on the day of ET had a significantly lower OPR but endometrial volume was not related with OPR. WHAT IS KNOWN ALREADY: A window of optimal serum P levels during the embryo implantation period has been described in artificial endometrium preparation cycles. A very low endometrial volume is related to poor reproductive outcome. STUDY DESIGN, SIZE, DURATION: Prospective cohort study with 244 patients who underwent ET in an oocyte donation cycle after an artificial endometrial preparation cycle with estradiol valerate and vaginal micronized progesterone (400 mg/12 h). The study period went from 22 February 2016 to 25 October 2016 (8 months). Sample size was calculated to detect a 20% difference in OPR (35-55%) between two groups according to serum P levels in a two-sided test (80% statistical power, 95% confidence interval (CI)). PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients undergoing their first/second oocyte donation cycle, aged < 50, BMI < 30 kg/m(2), triple layer endometrium > 6.5 mm and 1-2 good quality transferred blastocysts. A private infertility centre. Serum P determination and 3D ultrasound of uterine cavity were performed on the day of ET. Endometrial volume measurements were taken using a virtual organ computer-aided analysis (VOCAL T) system. The primary endpoint was OPR beyond pregnancy week 12. MAIN RESULTS AND ROLE OF CHANCE: About 211 of the 244 recruited patients fulfilled all the inclusion/exclusion criteria. Mean serum P on the day of embryo transfer was 12.7 +/- 5.4 ng/ml (Centiles 25, 9.2; 50, 11.8; 75,15.8). OPRs according to serum P quartiles were: Q1: 32.7%; Q2: 49.1%; Q3: 58.5%; Q4: 50.9%. The OPR of Q1 was significantly lower than Q2-Q4: 32.7% versus 52.8%; P = 0.016; RR (95% CI): 0.62 (0.41-0.94). The mean endometrial volume was 3.4 +/- 1.9 ml. Serum P on the day of ET did not correlate with endometrial volume. A logistic regression analysis, adjusted for all the potential confounders, showed that OPR significantly lowered between women with serum P < 9.2 ng/ml versus = 9.2 ng/ml (OR: 0.297; 95% CI: 0.113-0.779); P = 0.013. The ROC curve showed a significant predictive value of serum P levels on the day of ET for OPR, with an AUC (95% CI) = 0.59 (0.51-0.67). LIMITATIONS, REASONS FOR CAUTION: Only the women with normal uterine cavity, appropriate endometrial thickness and good quality blastocysts transfer were included. Extrapolation to an unselected population or to other routes and/or doses of administering P needs to be validated. The role of endometrial volume could not be fully defined as very few patients presented a very low volume. WIDER IMPLICATIONS OF THE FINDINGS: The present study suggests a minimum threshold of serum P values on the day of ET that needs to be reached in artificial endometrial preparation cycles to optimize outcome. No upper threshold could be defined.