Number of embryos transferred and implantation

Multiple pregnancies are considered the most frequent and serious complication of assisted reproduction technology. To reduce the frequency of multiple pregnancies, several centers have adopted a policy of reducing the number of embryos transferred in the uterus, suggesting single embryo transfer. Even though a significant number of papers have been published on this issue, no general consensus exists on how many embryos to replace in the uterus and at which cleavage stage. We conducted a retrospective study on cycles performed throughout 2003, analyzing the relation between the number of embryos transferred and the pregnancy and implantation rates, evaluating also the role of the woman's age. No differences were found among the groups except in one-embryo transferred women, which were mostly natural cycles, for estradiol levels, number of mature oocytes retrieved, number of top quality embryos, and pregnancy rate. The implantation rate was significantly higher in the two-embryo transfers versus three-embryo transfers. We found higher pregnancy and implantation rates with similar multiple pregnancy rates in patients where only two embryos were transferred versus three embryos transfer when women were less than 35 years old. In women aged less than 35 years, which in turn have the higher expectancy of successful pregnancy and also the higher risk of multiple pregnancy, the single embryo transfer is a suitable choice for these patients.