Endometrial compaction (decreased thickness) in response to progesterone results in optimal pregnancy outcome in frozen-thawed embryo transfers

Objective: To evaluate whether the change in endometrial thickness between the end of the estrogen phase and the day of embryo transfer has an impact on the pregnancy rate in frozen-thawed embryo transfer (FET) cycles. Design: Retrospective observational cohort study. Setting: Single tertiary care medical center. Patient(s): Ultrasound images in 274 FET cycles were reviewed. All patients underwent endometrial preparation with the use of hormonal therapy. Interventions(s): Ultrasound measurements of endometrial thickness at the end of the estrogen phase and the day of embryo transfer. Main Outcome Measure(s): The change in endometrial thickness and ongoing pregnancy rate. Result(s): We calculated the ongoing pregnancy rate in patients whose endometrial thickness decreased (compacted) after starting progesterone by 5%, 10%, 15%, or 20% compared with patients with no change or increased endometrial thickness. The ongoing pregnancy rate was significantly increased at all levels of compaction compared with no compaction. The ongoing pregnancy rate showed a significant increase with each decreasing quartile of change in thickness (increased percentage of compaction) in the progesterone phase compared with the estrogen phase.