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The outcomes of 1028 assisted reproductive technology cycles were studied retrospectively, considering two different periods of embryo transfer. In the first period, 262 cycles in women36 years old were studied, in which three embryos were transferred, followed by 157 cycles in womenor = 36 years, in which four embryos were transferred. In the second period, 332 cycles were evaluated in women36 years and 277 cycles in womenor = 36 years old, reducing the number of embryos transferred to two and three respectively. Embryos were only scored morphologically, and the best embryos were chosen for transfer. In the first period, in women36 years old, a clinical pregnancy rate of 55.7% was achieved, compared with 42.5% in the second period (P0.01). In womenor = 36 years old, the first period of embryo transfer showed a clinical pregnancy rate of 39.5%, compared with 28.5% in the second period (P0.01). The number of twin pregnancies in the three groups of patients in whom one to four embryos were transferred was not significantly different (24.2, 28.4, 24.8%). It is concluded that even with the biases induced by a retrospective study, the reduction in the number of embryos transferred, from three to two in women36 years of age, and from four to three in womenor = 36 years of age, without any selection other than pre-transfer morphological score, adversely affects the outcome of treatment, without a significant reduction in twin gestation rate. Other strategies are to be implemented in gametes and embryo selection, and patients must be aware that, even with a reduction in pregnancy rate, the goal is to achieve a high cumulative pregnancy rate, reducing the complications induced by multiple pregnancies.