P-110 Effects of embryo culture under atmospheric oxygen concentration on cumulative live birth rate and birth weight

Abstract Study question The purpose of this study is to compare cumulative live birth rate and perinatal outcomes of embryos cultured in 20% oxygen and 5% oxygen. Summary answer Atmospheric oxygen concentration not only affects the quality of embryos, but also affects the cumulative live birth rate and birth weight after embryo transfer. What is known already Whether 5% oxygen culture can effectively improve the outcome of embryonic pregnancy is still controversial. There is a lack of scientific data support from a large sample, especially regarding the cumulative live birth outcome as the primary outcome. Study design, size, duration This retrospective study included patients who received in vitro fertilization (IVF) treatment with their own first oocyte retrieval cycles from 1 January 2016 through 31 November 2019, with transfer dates limited to 31 November 2020. Our final analytic cohort included 31,566 women. Participants/materials, setting, methods Embryos were cultured at 5% or 20% oxygen concentration until the third day for transplantation or freezing. If prolonged culture was required, embryos of both groups were transferred to the incubator with 5% oxygen concentration to the blastocyst stage until transplantation or freezing. Other laboratory and clinical procedures were consistent between the two groups. Main results and the role of chance The rate of high-quality embryos in the 5% oxygen group was significantly higher than that in the 20% oxygen group （0.51 ± 0.33 vs 0.49 ± 0.33; β = −0.03; 95%CI, −0.03–−0.02; P < 0.001), while the rate of slow-developing embryos was significantly lower （0.52 ± 0.31 vs 0.56 ± 0.31; β = 0.04; 95%CI, 0.03–0.05; P < 0.001). The cumulative live birth rate was significantly higher in the 5% oxygen group than in the 20% oxygen group (62.4% vs 58.6%; adjusted OR = 0.85; 95%CI, 0.81-0.90). The birth weight and Z score （birthweight corrected for gestational age at birth, gender and parity were significantly lower in the 5% oxygen group than in the 20% oxygen group (birth weight: 3.28 ± 0.48 vs 3.30 ± 0.50, adjusted OR = 0.022, 95%CI, 0.004-0.04; Z score: 0.22 ± 1.01 vs 0.26 ± 1.04, adjusted OR = 0.037, 95%CI, 0.001–0.074). No matter what age group, the cumulative live birth rate, pregnancy rate and good birth outcome of the 5% oxygen concentration group were higher than those of the 20% group, while the proportion of no transferable embryos was lower than those of the 20% group. Limitations, reasons for caution Limitations include that oocytes were cultured at 20% oxygen concentration on the fertilization day (D0), and randomly distributed to incubators with different oxygen concentrations until day 1. Because it was a retrospective study, the grouping was not randomized. Wider implications of the findings We counted the largest sample data at present, took the cumulative live birth rate as the main outcome indicator, and tracked the perinatal outcome, using reliable data to prove that atmospheric oxygen concentration has serious and long-term irreversible effects on embryonic development. Trial registration number not applicable