The use of single embryo transfer to reduce the incidence of twins: Implications and questions for practice from the 'towardSET?' project.

In vitro fertilisation treatments where multiple embryos are transferred are associated with high multiple birth rates leading to a corresponding high infant morbidity. Here we review the results from a multidisciplinary project which aimed to combine state of the art statistical modelling of routine clinical data with consideration of patient perspectives to explore options for reducing multiple birth incidence by increased use of single embryo transfer (SET). Modelling was based on a large multicentre cohort, supplemented by analysis of HFEA register data. Patient perspectives were explored in qualitative interviews and focus groups. The data confirm the reduction of around one-third in the chance of a live birth for any couple in moving from double embryo transfer (DET) to SET in a fresh cycle. This can be somewhat offset by appropriate patient and cycle selection for SET, with many suggested schemes performing similarly, although many patients perceive such selection as unfair. If we take a complete cycle perspective, and consider the transfer of all good-quality embryos with cryopreservation then it is possible for SET to match or even outperform DET. However, the additional treatment cycles are seen by patients as physically and emotionally burdensome. Such treatments will require optimisation of embryo freezing policies and a number of options are explored.