Endometrial morphology and modulation of hormone receptors during ovarian stimulation for assisted reproductive technology cycles

ObjectiveTo study the biochemical and morphologic implications of different hormonal levels on endometrial development during assisted reproductive technology (ART) cycles.DesignProspective, controlled study.SettingUniversity center.Patient(s)Eleven women during a natural cycle (controls) and 11 oocyte donors during an ART cycle (treated).Intervention(s)At the time consistent with day-3 ET, a transvaginal ultrasound, an endometrial biopsy, and blood sampling were performed. Morphology and thickness of the endometrial stripe were recorded. Real-time reverse transcriptase–polymerase chain reaction was used to measure messenger RNA (mRNA) levels for estrogen receptor (ER)-α, ER-β, P receptor (PR)-A, and PR-B in the endometrial tissue.Main Outcome Measure(s)To evaluate morphologic and biochemical endometrial development.Result(s)Endometrium was mostly trilaminar (proliferative-like pattern) and thicker in the treated group, as opposed to homogeneous and thinner in the controls. The PR-B mRNA expression increased 41% in treated patients; PR-A mRNA expression, instead, was unchanged. Serum E2 and P were higher in the treated group than in controls. In contrast, FSH and LH levels were lower in the treated group.Conclusion(s)When compared with natural cycles, exposure of the endometrium to high hormone levels during ovarian stimulation significantly increased PR-B receptor expression at the time of ET. Concurrently, a proliferative-like endometrial pattern persisted. These findings reflect a delayed endometrial development in ART.