Selecting the 'best' embryos: prospects for improvement.

This review considers why and how embryos are selected for transfer and with what consequences. It concludes that: (i) current selection methods are inadequate or at least inadequately subjected to evidential scrutiny; (ii) decisions about number of embryos should be based not solely on input (numbers transferred) but on the likelihood of the transfer resulting in multiple pregnancies - out turn; and (iii) what is needed are better methods not just for selecting better embryos, but also for selecting responsible clinicians who collude less with their patients' demands but advise them more responsibly.