by Christine Briton-Jones

Created on: November 20, 2007   Last Updated: September 12, 2009

From single embryo transfer to elective single embryo transfer, current technology has changed the perception surrounding the transfer of only one embryo. The goal of reproductive endocrinologists using assisted reproductive technology (ART) has always been to increase the chances of achieving a healthy live singleton birth for their patients. In the earliest days of ART, the potential risks of multiple pregnancies were rarely a concern. In the 1970s emphasis was placed on being able to reliably collect one or two oocytes as treatment cycles commonly led to early failure due to no oocytes being recovered or only a single oocyte being recovered but failing to fertilize. The transfer of a single embryo was common but also associated with very disappointing pregnancy rates, particularly if calculated by the number of cycles started as many patients failed to achieve transfer at all.

In the 1980s controlled ovarian stimulation regimes developed and brought the ability to not only allow multiple ovarian follicles to develop to maturity but to also control the endogenous luteinizing hormone (LH) surge which often led to ovulation and loss of oocytes prior to retrieval. During this period of rapid increases in the pregnancy rates for each treatment cycle started, as successful oocyte retrieval became very reliable, a new dilemma was introduced. Greater pregnancy rates were achieved with the transfer of more than one embryo, which historically was often the only number of embryos available for transfer, now the transfer of three or four embryos became commonplace. Unfortunately multiple pregnancies consequently became commonplace as well.

Perinatologists pointed accusing fingers at reproductive endocrinologists for their apparent lack of regard for the complications of multiple pregnancies. The villains of the late 1980s were quadruplets, the 1990s identified the reality of the seriousness of triplet pregnancies and now twin pregnancies once passed off as being acceptable are being exposed for the health, financial and social costs they bring. Long held views that the transfer of a single embryo would surely lead to pregnancy failure persisted despite dramatic advances in both medical and laboratory technology during the 1990s and early 2000s.

An important vehicle for rapid improvement in success rates for assisted reproductive treatment was the development of sequential culture. The current view embryologists take is to develop the philosophy of a culture system rather

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