Day 7 blastocysts of infertility patients with only slow embryo development have reduced implantation potential despite chromosome euploidy

Abstract Research Question : To determine the reproductive potential of embryos that achieve blastulation on Day 7 (D7) followed by PGT-A for infertility patients that have slow embryo development. Design : Retrospective cohort study in a private IVF clinic of consecutive female infertility patients (n=2966) aged 24-48 (36.3±3.8) years who underwent frozen embryo transfer (FET) of a single euploid blastocyst. Results : Patients underwent single euploid FET of an embryo that achieved blastulation on Day 5 (D5, n=1880), Day 6 (D6, n=986) or D7 (n=100). D7 embryos resulted in lower implantation and live birth rates compared to both D5 and D6 embryos (p Conclusions : Euploid D7 embryos represented reduced implantation potential, even when controlling for maternal age. Of all D7 embryos that underwent PGT-A, euploidy was associated with expansion grade 5 or 6 and trophectoderm grade A. These results can help providers manage patient expectations in cases where infertility patients have slow embryo development.