Fresh Versus Frozen Embryo Transfer
In vitro fertilization (IVF) has three prerequisites for successful implantation: a healthy embryo; a properly built, receptive endometrium; and adequate synchronization. To obtain several oocytes/embryos, controlled ovarian stimulation is applied, and in contrast to a natural cycle, this causes steroid hormones to rise to supraphysiologic levels. This can induce accelerated endometrial changes, premature luteinization, and altered gene expression.[1,2] These undesired effects also can hinder implantation.
Decades of research have focused on methods to identify the embryo with the highest implantation potential.[3] Only very recently have the benefits of alternative methods of embryo transfer (eg, freezing all with delayed transfer) been assessed.[4] A recent meta-analysis[5] compared clinical outcomes with fresh versus frozen embryo transfer (as part of a freeze-all cycle strategy) in women with different degrees of ovarian response.
Data from 5265 patients who took part in eight randomized controlled trials of IVF were included in the meta-analysis. The investigators compared the outcomes of fresh embryo versus first frozen embryo transfer in normal and high ovarian responders.
The number of oocytes and metaphase II oocytes retrieved were comparable among normal and high responders. The number of fertilized oocytes was similar after fresh and frozen embryo transfer cycles in high responders, but in normal responders, fewer oocytes were retrieved from frozen embryo transfer cycles.
