Reproductive Medicine & Window of (Embryo) Implantation

Scientific presentation by the group of Zech Nicolas, 2016 (

 Improving synchronicity between embryo and endometrium for slow developing embryos by transfer in vitrified/warmed IVF-cycles

Introduction: The window of implantation (WOI) specifies the short time in which the endometrium becomes receptive for the embryo, opening around 5 days after ovulation predominantly by progesterone. WOI is suggested as an interval of 2-4 days and might differ between individuals. Transfer of expanded blastocysts on day 5 ensures an optimal synchronicity between embryo and endometrium, whereas fresh embryo transfer of slow developing embryos (SDE) result in low implantation rates (IR). Aim of the study was to analyze whether vitrified/warmed embryo transfer in combination with prolonged embryo culture improves implantation of SDE.

Methods: In a retrospective single-center study we evaluated clinical outcome after fresh (group A, n=636) or vitrified/warmed transfer of SDE without prolonged embryo culture (group B, n=60) or with prolonged embryo culture before transfer (group C, n=244). All transfers were performed under luteal phase support in a day 5 endometrium.

Results: Transfer of top-quality SDE (early blastocysts formed by many cells without excluded blastomeres) resulted in IR of 21.2%, 20.7%, 20.7% and birth rates (BR) of 25.4%, 31.3%, 23.9% in Group A, B or C, respectively. With non-top quality SDE (non-top early blastocysts, morulae or compacting embryos) IR of 5.5%, 16.7%, 20.2% and BR of 5.5%, 21.4%, 22.5% were observed.

Conclusions: Vitrification and transfer of non-top SDE in cryo-cycles improves IR and BR, suggesting a better luteal phase synchronicity resulting in a more receptive endometrium. A better synchronization between embryo development and endometrium is hypothesized to be responsible for this finding.

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