Are there associations between clinical and embryological factors with pregnancy loss following transfer of a single euploid embryo?

First-trimester pregnancy losses are commonly attributed to chromosomal abnormalities. The causes of pregnancy loss following transfer of a euploid embryo are not fully elucidated. The aim of this study was to evaluate clinical and embryological parameters for pregnancy failure following the transfer of a single euploid embryo. Pregnancy outcomes of single euploid embryo transfers from a single centre between January 2017 and March 2020 were retrospectively evaluated. Several clinical and embryological parameters were evaluated in consideration to pregnancy outcomes; total pregnancy loss and live birth (LB). Endometrial preparation type, number of previous frozen embryo transfer cycles, history of recurrent pregnancy loss, higher body mass index, presence of endometriosis and/or adenomyosis and embryo quality were found to be significantly different between two groups. Morphokinetic parameter analysis of 523 euploid embryos using time-lapse imaging did not show any statistical differences between the two groups; however, a significantly higher rate of uneven blastomeres in the cleavage stage was observed in the total pregnancy loss group. Evaluation of clinical and embryological data can reveal possible factors associated with pregnancy loss that can facilitate improved patient consultation. Feasible interventions can potentially increase the chance of achieving an LB. Lay Abstract Like natural pregnancies, not all pregnancies following fertility treatment go to term. The most common reason for these losses is that these embryos lack the genetic constitution compatible with live birth. Combined with fertility treatment, genetic tests can evaluate the genetic ability of embryos to go to term. Monitoring the outcome of pregnancies resulting from such embryos can help us identify whether and which conditions specific to treatment can lead to pregnancy loss. The analysis identified four parameters associated with embryo loss: Embryo quality and division patterns, existence of previous treatment and treatment type.