Prevention of twin pregnancies after IVF/ICSI by single embryo transfer

Twin pregnancies constitute the most serious complication for both mother a nd children after IVF/ICSI treatment, but transfer of at least two 'best lo oking' embryos remains the standard policy. This is due to our inability an d reluctance to identify both the 'twin prone' patient and the top quality embryo. Some centres now electively transfer a single embryo (eSET) when pa rticular embryo quality and patient criteria are met. Results from several centres were presented during an ESHRE Campus Course, held on May 6th 2000. Sound clinical trials are needed to clarify several points of discussion. What is the clinical profile of patients in whom eSET should be considered? Will the overall (ongoing) pregnancy rate of the IVF/ICSI programme decrea se if eSET is performed in these patients? What is the twinning rate when e SET is a routine policy? Will the financial gain by avoiding perinatal hosp italization costs of prevented twins be balanced by the likely need to perf orm a number of extra IVF/ICSI cycles? What will be gained by freezing the extra number of high quality embryos? Should eSET be performed at the 2 pro nuclear stage, the early cleaving embryo or the blastocyst stage? Common se nse dictates that eSET as a concept should be applied from now onwards.