Over the past 20 years, there has been a steady increase in birth rates resulting from in vitro fertilization (IVF). Despite the gradual reduction in the number of embryos transferred, twin birth rates remain very high in many countries, which poses risks to the health of both mothers and children. The selective transfer of a single embryo, chosen according to strict morphological criteria, combined with an effective embryo freezing program, could help prevent multiple births without reducing the chances of having a child, at least among the youngest and most fertile women. (R.A.)