Better late than never: the clinical value of Day 7 blastocysts.

Abstract

The advancement of in vitro culture media has improved the efficacy of ARTs in the treatment of infertility (Chronopoulou and Harper, 2015). Despite this progress, embryos may demonstrate delayed development and reach the blastocyst stage on Day 7. The prevalence of these slow embryos has been reported as 5% and even though they are considered to be less competent and reveal a lower euploidy rate than faster growing embryos, they are still capable of achieving high implantation and clinical pregnancy rates (Hammond et al., 2018). These slow-developing embryos could have clinical value in patients with reduced chance to achieve a live birth (LB) with their own oocytes. This clinical value has been demonstrated by the increased number of patients that obtain at least one transferable embryo following preimplantation genetic testing for aneuploidy (PGT-A) with the extension of culture to Day 7 (Capalbo et al., 2014; Cimadomo et al., 2018; Tiegs et al., 2019). Studies thus far exploring the extension of culture to Day 7 lack uniformity in defining the Day 7 embryo, as well as providing context toward the parameters for proceeding with extended culture, culture conditions, local regulations and clinical setting.