Pasternak MC, et al. - As disparity exists in interval growth between male and female embryos, researchers investigated the predictive value of cleavage stage morphology as observed via time-lapse microscopy, for the sex of an embryo. In this retrospective single-institution study, they recorded demographics of patients undergoing in vitro fertilization (IVF) with pre-implantation genetic testing for aneuploidy (PGT-A) during a 4-year period, as well as characteristics of the resultant embryos, including day 3 morphology and PGT-A results. They analyzed a total of 10,523 embryos from IVF/PGT-A cycles over 4 years. Via genetic testing, they identified 5352 embryos as female, vs 5171 as male. It is premised that routinely, embryos of one sex (male or female) may grow more rapidly, and therefore bias gender selection in institutions that perform fresh embryo transfer (ET) based upon cleavage stage morphology. Based on two criteria, they graded cleavage stage embryos, specifically the number of cells, and overall appearance of the embryo as often evaluated by fragmentation. Male vs female embryos showed no difference in morphological appearance, growth rate, or rate of euploid status. The data thereby suggest that no inherent sex bias exists based upon selection of the best morphologically appearing cleavage stage embryo for fresh ET.