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

Objective: To study the biochemical and morphologic implications of different hormonal levels on endometrial development during assisted reproductive technology (ART) cycles. Design: Prospective, controlled study. Setting: University 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 E ₂ 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.