No participants met the inclusion criteria in an exted period of time.

This study evaluates which transfer strategy will result in a higher probability of pregnancy in patients whose single best day 5 embryo resulting from an IVF cycle is classified as expansion grade <4 by Gardner and Schoolcraft classification. All cycles will be cultured to day 6 and half the patients will undergo a fresh embryo transfer and the other half a frozen embryo transfer.

A lack of established markers for predicting blastocyst development increases the risk of having no embryos or embryos not-fully expanded available for transfer. Slower but non-arrested embryos are frequently found to have progressed to blastocyst stage by the time of a day 6 transfer. In the absence of a receptive endometrium, embryo selection for fresh transfer may be futile, and cryopreservation could be a better option. The objective is to determine which transfer strategy will result in a higher probability of pregnancy in patients whose single best day 5 embryo resulting from an IVF cycle is classified as expansion grade <4 by Gardner and Schoolcraft classification. The investigators hypothesize that in bad prognosis patients with slow-developing blastocysts, vitrified-warmed embryo transfer will result in higher implantation, clinical and ongoing pregnancy and live birth rates than fresh embryo transfer.

Inclusion Criteria:

• All IVF cycles undergoing autologous fresh blastocyst embryo transfer
• All IVF cycles in which the best available embryo for transfer is at expansion grade <4
• All ages

Exclusion Criteria:

• Ovum Donation cycles
• Preimplantation genetic testing cycles

all collected IPD

January 2020

All