ABSTRACT
INTRODUCTION In vitro fertilization (IVF) programs are coming closer every day to the goal of reducing multiple pregnancies while maintaining good clinical results. e transfer of a single embryo is progressively becoming a reality, and this is the result of major improvements in dierent areas. From a clinical point of view, two major achievements are worth mentioning: first, physicians have learned to handle the stimulation drugs that are more pure, more powerful, and more comfortable for the patient; and second, an increased knowledge of the pathophysiology of ovarian hyperstimulation syndrome has made the frequency of this syndrome almost anecdotal. On the other hand, concerns about the “epidemic” of multiple gestations have raised awareness of the risks not only to the mother (gestational diabetes, hypertension, and anemia), but also to the babies-extreme prematurity, low birth weight, children with neurological damage, and so on-not to mention the psychological burden and suering of the parents and the tremendous health costs that it entails. From the laboratory point of view, several achievements are worth mentioning as well: studies on embryo metabolism have led to the formulation of suitable culture media. In the early 1990s, the introduction of intracytoplasmic sperm injection (ICSI) revolutionized the treatment of male infertility and genetic screening became the gold standard for the selection of aneuploid embryos. Vitrication came along, and preservation of fertility was no longer a utopia for modern women; the wave of the “omics” initiated an era of noninvasiveness for studying human embryos in the laboratory, and most recently, the introduction of imaging systems allowed us to assess embryos in a dierent way: through their morphokinetics.
