The Impact of Early Embryos Incubation on Pregnancy Rate in IVF (IVF-2010)

It has been common practice to cryopreserve surplus embryos achieved during IVF treatment or in other situation that embryos are to be preserved for other situations such as suspected ovarian hyper stimulation syndrome, fertility preservation or patient request.

Embryos are usually frozen on day 2, 3 or day 5-6 at the Blastocyst stage. At the time that thawing is planned, patients' cycle is synchronized and prepared either with hormonal treatment or at the natural cycle.

Not all embryos will always survive the thawing and sometimes they will all degenerate.

Embryos that survive the thawing procedure are assessed and replaced on the day of the thaw or left overnight for better selection and will be replaced only if they continue to divide in vitro.

The advantage of embryo transfer on the day of thaw is that embryo exposure in culture is shortened and embryo selection will be occurring in the womb. On the other hand, overnight incubation may avoid transferring embryos that potentially are not able to divide and are biologically not viable.

Although both attitudes are practiced in different IVF centers, at present there are no prospective randomized studies that have been conducted to advise which intervention is better in terms of pregnancy rates.

The purpose of the present study is to assess which technique will result in better pregnancy rates.