Transferring more than one embryo simultaneously is justifiable in most patients.

Elective single embryo transfer (eSET) was first introduced to IVF in 1999, and its subsequent integration into mainstream reproductive endocrinology and infertility has been hugely consequential. It can be viewed as the first (among many since) 'add-ons' to IVF that has significantly and adversely affected how IVF is practised, resulting in astonishing declines in live birth rates after fresh non-donor IVF cycles worldwide. We propose that, like most 'add-ons' to IVF over recent years, the almost universal use of eSET worldwide lacks proper validation of its underlying hypothesis and is based on statistically incorrect assumptions and incorrect data interpretation. As with most recent 'add-ons' to IVF, eSET lacks evidentiary support, and, therefore, its remarkable success in the marketplace must be based on expert opinions, the lowest level of evidence in medicine and widely recognized as frequently biased. Like other 'add-ons' to IVF, eSET-practice must be reassessed because it does not offer the benefits it has widely claimed to provide, prolongs time to conception and adversely affects live birth chances for many women. Moreover, by ignoring that infertile women value quick conception over most other considerations, provider-insistence on eSET frequently deprives them of the right to self-determination.