RESUMO
Objective To investigate the real correlation between embryo density and developmental outcome of cleavage embryos on day 3 by adjusting covariates. Methods Data of 1196 embryos from 206 couples undergoing in vitro fertilization and embryo transfer(IVF-ET) treatment were retrospectively analyzed. Embryos were hypoxia-cultivated in a fixed 30 μl microdrop in culture dishes. Embryo quality on day 3 was evaluated and proportion of good quality cleavage embryos on day 3 was used as the endpoint. Maternal age, paternal age, antral follicles, level of anti-mullerian hormone (AMH), type of infertility, controlled ovarian stimulation(COS) protocol, length of stimulation, number of retrieved oocytes, and type of insemination were chosen as covariates. Results A total of 1196 embryos were included and analyzed. Three embryo densities were routinely used: 30 μl/ embryo [1 embryo/ (30 μl·drop)], 15 μl/ embryo [2 embryos / (30 μl·drop)] and 10 μl/ embryo [3 embryos/ (30 μl·drop)]. The number of embryos assigned into these three groups were 434, 646 and 116 embryos separately. The average proportion of good quality embryos on day 3 in 10 μl/ embryo group were lower than that in both 15 and 30 μl/ embryo group (29. 31% vs 40. 25%,P 0. 05). In the regression analysis, without adjusting any covariables, the good quality embryos rate on day 3 of the 10 μl/ embryo group was 43% lower than that of the 30 μl/ embryo group (0. 57, 95% CI 0. 32, 1. 03), and there was no statistical difference (P>0. 05). In the minimum-adjusted model 2 (adjusted the level of AMH and type of insemination), proportion of good quality embryos on day 3 in group of 10 μl/ embryo significantly decreased by 51% (0. 49, 95% CI 0. 27,0. 90, P < 0. 05) compared with that in group of 30 μl/ embryo. Conclusion In a 30 μl microdrop, compared with individual cul turing, group culturing with the density of 10 μl / embryo did not benefit the development of the cleavage embryos and 30 μl / embryo was the optimal embryo density.