The need for new methods of ovarian stimulation.

It is easy to diagnose sterility but much harder to diagnose subfertility, because minor defects are not necessarily associated with consistent impairment of fertility. Correct evaluation of the background fertility can avoid needless treatment of couples. Ovarian stimulation is a powerful strategy frequently used to re-establish or improve fertility in infertile couples, but it is often the cause of twin pregnancy. The risks and costs of multiple gestation are important factors that must be taken into full account in the pro-fertility decision. To avoid twins, inseminations should preferably be done in unstimulated cycles or in association with induced mono-ovulatory cycles. For the same reason, it is probably time to follow the policy of favouring single embryo transfer in young women undergoing IVF and intracytoplasmic sperm injection programmes. In addition, there is an urgent need to avoid an invasive multiple transfer policy in women over 38 and to select new strategies to improve the well-known age-related lower implantation rate.