O-236 Fatty acid supplementation into warming solutions improves pregnancy outcomes after single vitrified-warmed cleavage stage embryo transfer

Abstract Study question Does fatty acid (FA) supplementation into warming solutions affect pre-implantation development, outgrowth competence, and clinical outcomes of human vitrified cleavage stage embryos? Summary answer FA-supplemented solutions improve morphology and outgrowth of blastocysts derived from vitrified cleavage stage embryos and pregnancy outcomes after single vitrified-warmed cleavage stage embryo transfer (SVCT). What is known already Vitrification procedure decreased the intracellular lipid content and subsequent developmental competence. Furthermore, a recent study reported that FA supplementation into warming solutions increased intracellular lipid content and improved developmental competence by stimulating the beta-oxidation pathway in mice and bovines. However, in humans, the effects of FA addition to warming solutions on developmental competence and morphokinetics during the pre-implantation period remain unknown. Additionally, the efficacy of FA supplemented warming solutions in clinical settings has not yet been evaluated. Study design, size, duration A total of 217 discarded human vitrified 4-cell stage embryos donated for research by consenting couples were randomly allocated, to be warmed in solutions either with (FA, n = 111) or without FA (control, n = 106). Embryonic development, morphokinetics, and trophoblast migration were experimentally compared between the groups. Furthermore, a total of 701 clinical records of women who underwent SVCT between April and September 2022 were retrospectively analysed (control, April–June; FA, July–September). Participants/materials, setting, methods Discarded 4-cell stage embryos were warmed and cultured for 72 h in a time-lapse incubator. Furthermore, the blastocysts produced were plated on fibronectin-coated dishes and cultured to assess blastocyst adhesion and outgrowth. In the clinical study, vitrified cleavage stage embryos were warmed in solutions with or without FA and transferred on day 2 after ovulation in the natural cycle. The rates of implantation, clinical pregnancy, and ongoing pregnancy were compared between the groups. Main results and the role of chance The developmental rates were comparable between the groups. However, the rate of morphologically good blastocysts was significantly higher in the FA group than in the control group (P = 0.0089). The developmental timings were comparable between the groups during all stages. Additionally, the incidence of abnormal cleavages, amount of fragmentation at the cleavage and morula stages, and incidence of blastomere exclusion or extrusion during peri-compaction were comparable between the groups. Further, the blastocyst adhesion rate after outgrowth culture was also comparable between the groups. However, the outgrowth area was significantly larger in the FA group than in the control group (P = 0.0438). In the clinical study, the characteristics of the patients and transferred embryos were comparable between the groups. The implantation, clinical pregnancy, and ongoing pregnancy rates were higher in the FA group than in the control group (P = 0.0252, P = 0.0223, and P = 0.0281, respectively). Multivariate logistic regression analysis demonstrated that the probability of ongoing pregnancy was significantly higher in the FA group than in the control group (adjusted odds ratio, 1.46; 95% confidence interval, 1.02–2.06; P = 0.0340). The rate of miscarriage during the first trimester was comparable between the groups. Limitations, reasons for caution This study has some limitations owing to its retrospective design. Further prospective studies are required to validate the clinical efficacy of FA-supplemented solutions. Furthermore, the effects of adding FA to warming solutions on maternal and perinatal outcomes should be assessed in the future. Wider implications of the findings FA supplementation into warming solutions would improve the clinical outcomes of frozen embryo transfers, leading to a shortened treatment period and reduced patient burden in assisted reproductive technologies. Trial registration number not applicable