Abstract: BACKGROUND: A large number of previous studies have confirmed that a high concentration of metabolites is significantly correlated with embryo quality and clinical outcome, and the theory of silencing embryo development indicates that normally developed embryos maintain a low level of material exchange with the outside world during in vitro culture, while embryos often show abnormal metabolic activity due to stress repair mechanism when DNA damage occurs. 
OBJECTIVE: To establish and verify an embryo quality prediction model based on the third-day 340 nm absorbance embryo cultures to provide the basis for a more objective and accurate embryo quality assessment. 
METHODS: 269 patients at the Nanxishan Hospital of Guangxi Zhuang Autonomous Region for in vitro fertilization and embryo transplantation from November 2019 to December 2021 were retrospectively analyzed. Among them, on day 3, 162 cases who had 873 optimal embryos and 214 high-quality blastocysts were included in the high-quality embryo group. On day 3, 107 cases who had 859 non-optimal embryos and 214 non-high-quality blastocysts were included in the non-high-quality embryo group. Lambert-beer law was used to screen out the characteristic wavelength with distinguishing degree between superior and non-superior embryos, analyze its correlation and influence trend with high-quality embryos, and establish the clinical prediction model and validation of absorbance for high-quality and non-high-quality embryos at this wavelength.
RESULTS AND CONCLUSION: (1) There was a significant difference in absorbance between high-quality and non-high-quality embryos at 340 nm on day 3 (P < 0.001), and a negative correlation was found with the formation of high-quality embryos on day 3 (r=-0.486, P < 0.001). The absorbance of high-quality and non-high-quality blastocyst at 340 nm was significantly different (P < 0.05), and was negatively correlated with the formation of high-quality blastocyst (r=-0.642, P < 0.001). (2) The optimal cut-off value of absorbance at 340 nm between high-quality and non-high-quality embryos on day 3 was 0.235. The area under the curve was 0.799. Sensitivity was 62.9%. Specificity was 78.0%. Accuracy was 70.5%. The optimum cutoff value of high-quality and non-high-quality blastocysts of absorbance at 340 nm was 0.175. The area under the curve was 0.871. Sensitivity was 74.3%. Specificity was 89.1%. Accuracy was 82.2%. (3) Restricted cubic spline curve analysis showed that when the absorbance of the culture medium at 340 nm was greater than 0.221, there was a significant positive trend on the formation of non-high-quality embryos at day 3, and when the absorbance of the culture medium at 340 nm was greater than 0.160, there was a significant positive trend on the formation of non-high-quality blastocysts. (4) The clinical decision curve and clinical influence curve showed that the absorbance of the culture medium at 340 nm had the maximum clinical net benefit for the prediction models of high-quality embryos and high-quality blastocysts on the third day when the valve probability was 0.18-0.95 and 0.16-1.00, respectively, and the ratio of loss to gain within the valve probability range was always less than 1. It is proven that the prediction model has good efficacy in clinical applications. The results of embryo transfer showed that the absorbance of embryo culture medium at 340 nm in non-pregnant patients was significantly higher than that in clinical pregnancy, biochemical pregnancy and early abortion patients (P < 0.05). (5) The high-quality and non-high-quality embryo culture in 340 nm absorbance has a significant difference with correlation. The embryo quality prediction model has a certain clinical value and application effectiveness. The joint embryo morphology evaluation to a certain extent improves the objectivity and accuracy of embryo quality evaluation.

Key words: embryo quality assessment, embryo metabolomics, embryo morphology evaluation, prediction model, high-quality embryo