Evaluating the heterogeneous effect of extended incubation to blastocyst transfer on the implantation outcome via causal inference

ABSTRACT In IVF treatments, extended culture to single blastocyst-transfer is the recommended protocol over cleavage-stage transfer. However, evidence-based criteria for assessing the heterogeneous implications on implantation outcome are lacking. To estimate the causal effect of blastocyst-transfer on implantation outcome, we assembled a multicenter dataset of embryo time-lapse imaging. The data includes a natural source of randomness and has a strong claim for satisfying the assumptions needed for valid causal inference. By fitting a causal forest model, we assessed the ‘ Transfer Lift ’, which quantifies the probability difference in embryo implantation if transferred as a blastocyst versus cleavage-stage. Blastocyst transfer increased the average implantation rate, however we revealed a subpopulation of negative Transfer Lift embryos whose implantation potential is predicted to increase via cleavage-stage transfer. We provide day-of-transfer decision-support tools that are retrospectively estimated to improve implantation rate by 32%, thus demonstrating the efficacy of embryo-level causal inference in reproductive medicine. One Sentence Summary A causal inference model predicts the heterogeneous effect of prolonged incubation to blastocyst transfer on embryo implantation, thus providing means for optimizing pregnancy rates in IVF treatments.