Embryo grading
The presence of two clearly distinct pronuclei, together with two individualized or fragmented polar bodies, 20 hours after IVF/ICSI, was considered normal fertilization. Day 3 embryos with 7–9 equal-sized cells, < 10% degree of fragmentation rate, were defined as high-quality embryos (HQE). Day 3 embryos with eight equal size blastomeres and no cytoplasmic fragments, derived from day 2 embryos with four equal size blastomeres and no cytoplasmic fragments were defined as top-quality embryos (TQE)17.