[Frozen embryo transfer protocol: does spontaneous cycle give good results?]

Frozen embryos' transfer optimize the pregnancy rates per retrieval. In France, 60% of transfer cycles occur in stimulated cycles. The aim of this study was to evaluate the outcomes of frozen embryo transfers in spontaneous, substituted and stimulated cycle.

This retrospective study includes patients who are 18-43 years old and had a frozen embryo transfer between 1st January 2008 and 31st December 2008. Three transfer protocols have been used: the spontaneous cycle (group 1), substituted cycle (group 2), and stimulated cycle (group 3). The characteristics of couples, embryonic parameters and data transfer cycles, and their outcomes were evaluated.

Among the 333 patients, 132 were included in the first group, 24 in the second group and 177 in the third group. After checking the homogeneity of the three groups, we found pregnancy rates (respectively 20.49 vs 13.04% and 11.32%, P=0.0348), and deliveries (respectively 13.93 vs 8,7 and 6.29%, P=0.0314), significantly higher in spontaneous cycles.

Currently there is no consensus on the best technique for endometrial preparation for frozen embryo transfer. Our results support transfers in spontaneous cycle for normo-ovulating patients. Natural cycles can achieve good pregnancy rates while minimizing the costs and side effects.