Disposition of extra embryos

Contemporary practice in assisted reproductive technologies (ART) compensates for the attrition that occurs at each phase of the cycle. Every follicle does not yield an egg, nor does every egg fertilize. Of those that do, many fail to properly develop, and even fewer implant. Nevertheless, ART cycles usually result in more embryos than are needed for transfer. With clinical and laboratory advances in the field and the undeniable need to reduce the incidence of multiple gestation, we must focus increased attention on these “spare” or “extra” embryos and their fate.

The relative quality of extra embryos clearly influences their disposition. Although the pregnancy potential of any single embryo is always uncertain, a fragmented embryo from a patient over the age of 40 generally has less potential than a morphologically normal one from an egg donor. Data from 1996 SART registry (1) suggests that only 4% of transferred embryos from patients 39 years and older result in a child, whereas this number is approximately 12% in women under 35. Because most programs choose the highest quality embryos for transfer, potential implantation rates for spare embryos would be lower.

Registry data are invaluable to track progress in the field, but they do little to guide decisions concerning individual patients, because the implantation rate of any given embryo of reasonable morphology is either zero or 100%. In the absence of more reliable markers of implantation potential, we must assume that all transferred embryos can implant. . .