ENDOMETRIAL PREPARATION - LESSONS FROM OOCYTE DONATION

Objective: To gain insight into the physiology of human endometrial de velopment after artificial preparation with estrogen (E) and P, before oocyte donation. Design: Review and analysis of relevant studies publ ished in the last decade, identified through the literature and Medlin e searches. Results: Oocyte donation represents a unique in vivo exper imental model in the human that permits the study of endometrial devel opment under controlled variable conditions. Early studies have shown that adequate endometrial preparation can be achieved by sequential E and P only. The successful implementation of the simplified approach t o oocyte donation demonstrated that satisfactory endometrial receptivi ty is not dependent on incremental administration of E and P and simil arly can be achieved by fixed dosages of these steroids. Moreover, num erous clinical oocyte donation studies have shown that both physiologi c and supraphysiologic levels of E and P have resulted in good endomet rial development and pregnancy rates, underlining the relative insensi tivity of the endometrium to extreme hormonal conditions. In addition, it has been clarified that the endometrium is tolerant of some manipu lations during the follicular phase. Contrary to morphological studies that demonstrated preservation of endometrial preparation after lutea l E depletion, preliminary evidence suggests that the functional capac ity of the endometrium could be affected adversely. Conclusion: In con trast to early oocyte donation studies, which indicated a correlation between morphologic integrity and functional capacity of the endometri um, some evidence presented in this review demonstrates that adequate endometrial morphology does not always imply normal endometrial recept ivity.