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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.
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<p><b>OBJECTIVE</b>To explore an optimal model of hypothetical work injury insurance scheme, which is in line with the wishes of workers, based on the problems in the implementation of work injury insurance in China and to provide useful information for relevant policy makers.</p><p><b>METHODS</b>Multistage cluster sampling was used to select subjects: first, 9 small, medium, and large enterprises were selected from three cities (counties) in Zhejiang Province, China according to the economic development, transportation, and cooperation; then, 31 workshops were randomly selected from the 9 enterprises. Face-to-face interviews were conducted by trained interviewers using a pre-designed questionnaire among all workers in the 31 workshops.</p><p><b>RESULTS</b>After optimization of hypothetical work injury insurance scheme, the willingness to participate in the scheme increased from 73.87%to 80.96%; the average willingness to pay for the scheme increased from 2.21% (51.77 yuan) to 2.38% of monthly wage (54.93 Yuan); the median willingness to pay for the scheme increased from 1% to 1.2% of monthly wage, but decreased from 35 yuan to 30 yuan. The optimal model of hypothetical work injury insurance scheme covers all national and provincial statutory occupational diseases and work accidents, as well as consultations about occupational diseases. The scheme is supposed to be implemented worldwide by the National Social Security Department, without regional differences. The premium is borne by the state, enterprises, and individuals, and an independent insurance fund is kept in the lifetime personal account for each of insured individuals. The premium is not refunded in any event. Compensation for occupational diseases or work accidents is unrelated to the enterprises of the insured workers but related to the length of insurance. The insurance becomes effective one year after enrollment, while it is put into effect immediately after the occupational disease or accident occurs.</p><p><b>CONCLUSION</b>The optimal model of hypothetical work injury insurance scheme actually realizes cross-regional mobility of workers, minimizes regional differences, and embodies the fairness. The proposed model will, to some extent, protect the rights and interests of enterprises, as well as the healthy rights and interests of workers when they are unemployed.</p>