Abstract
The gold standard in endometrial preparation remains what has been established for oocyte donation receivers. This preparation requires E2 for 14 days and then P4 in isolation. Endometrial thickness can now be evaluated with three-dimensional ultrasound or with the VOCAL system, which can evaluate endometrial volume: however, the mean thickness of the endometrium only has a predictive value for pregnancy at 6 mm, on day 6 or on the day that hCG is triggered. Despite the technical progress made, Doppler ultrasound, which can evaluate endometrial and subendometrial blood flow, does not contribute valid responses as to uterine receptivity and the chances for pregnancy. However, the level of uterine contractions at embryo transfer is recognized as a major factor of implantation and, to obtain faster uterine quiescence, it is recommended to begin progesterone before the transfer. The need for prolonged progesterone maintenance in case of pregnancy continues to be debated.
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