Biological predictive criteria for clinical pregnancy after elective single embryo transfer.

In this prospective observational study, the onset of a clinical pregnancy after elective single embryo transfer (eSET) was significantly associated with: 1) the woman's age as well as the number of good- and top-quality embryos; and 2) the day of the embryo transfer (day 3>day 2). Good-quality embryos had the same ability to implant, regardless of the zygotic score, the day 1 early cleavage rate, the fragmentation degree, and the top-quality assessment, specifying the eligibility criteria for eSET.