Defining women who are prone to have twins in in vitro fertilization--a necessary step towards single embryo transfer

PURPOSE: The aim of the present study was to identify subsets of women undergoing two-embryo transfer in in vitro fertilization (IVF) who are prone to give birth to twins. METHODS: During 1990 to 2002 4580 day 2 or day 3 two-embryo transfers were conducted and these constituted the study population. RESULTS: By selecting combinations of factors, some subsets of patients where single-embryo transfer might be conducted would reduce the estimated twin rate by 60%, but requiring single-embryo transfer in only approximately one third of the patients. Examples of such selected groups were patients less than 33 years of age with two top quality embryos, patients less than 39 years of age with two top quality embryos and conducting their first IVF cycle, and patients less than 39 years of age with two top quality embryos and two optimal cleavage cells. CONCLUSION: By combining factors, subsets of patients with both a high birth and twin rate that could be recommended single embryo transfer were identified.