Does Length of Preparation Phase in Medicated Vitrified-Warmed Single Blastocyst Transfer Cycles Affect Cycle`s Outcome? A Cohort Study

Objective: To assess whether the outcome of vitrified-warmed single blastocyst transfer (SBT) is affected by the length of the medicated lining preparation period.

Materials and methods: A retrospective cohort study performed at a single academic reproductive center. All vitrified-warmed SBT conducted between 2012 and 2014 were reviewed. Preparation protocol included 6mg Estradiol valerate tablets daily starting day 2-3 of cycle. First monitoring visit was flexible upon treating physician decision. Initiation of vaginal progesterone was usually indicated when lining measurement had reached 8mm or more. Embryo transfer was scheduled after completing 5 days of vaginal Progesterone. Data regarding demographic background, subfertility diagnosis and cycle characteristics, including outcome, were collected. Primary outcomes were clinical pregnancy and live birth, which were tested in a multivariate model correcting for cycle length.

Results: During the study period 1428 vitrified-warmed SBT cycles were conducted. Mean length of proliferative phase was 12.8 ±3.5 days, ranging from 4 to 32 days, 10th percentile being 10 days, 90th percentile being 17 days. Mean lining width was 9.6 ±3.2 mm. Outcome rates were as following: pregnancy rate 47.9%, clinical pregnancy rate 34.6% and live birth rate 21.1%. In multivariate logistic regression model, clinical pregnancy and birth were not affected by stimulation length. The model included patients` age, infertility diagnosis, parity, endometrial width and days of preparation. Age and embryo quality were the only variables affecting the outcomes tested.

Conclusion: Clinical pregnancy and live birth achieved in A vitrified-warmed SBT cycle are not affected by the length of endometrial preparation period.