BACKGROUND: Increasing use of IVF in the USA has been a major contributor to the rising national multiple birth rate. Many have advocated that reducing the number of embryos transferred is essential for addressing the IVF-associated multiple birth problem. METHODS: A population-based sample of 506 072 IVF transfers performed in the USA in 1996-2002 was used to investigate trends in embryo transfer practices and to determine whether any changes in practice patterns have impacted the multiple gestation risk associated with IVF. RESULTS: The proportion of procedures in which >or=3 embryos were transferred declined significantly for most patient groups between 1996 and 2002. However, declines for some groups were not sizeable (from 79 to 73% and from 76 to 71% for fresh, non-donor procedures among women aged 38-40 and 41-42 years respectively) and transferring >or=3 embryos remained the norm for all groups. As of 2002, single embryo transfer had not increased for most groups and remained uncommon. Some declines in overall multiple gestation rates were observed, although multiple gestation risk associated with 2 embryos transferred increased significantly for all groups. CONCLUSIONS: Despite changes in embryo transfer practices, multiple gestation risk remains high, in part due to increased multiple gestation rates associated with the transfer of two embryos.