Inter- and Intra-Observer Agreement Between Embryologists for Cytoplasmic String Assessment in Day 5/6 Human Blastocysts.

To investigate inter- and intra-observer agreement in the assessment of cytoplasmic string (CS) by embryologists on day 5/6 human blastocysts using the EmbryoViewer software. This was a prospective study involving five embryologists working between 2019 and 2020. Inter-observer agreement was calculated using assessments performed on 104 day 5/6 blastocysts regarding the presence, number, and location of CS and CS vesicle activity using timelapse videos. Intra-observer agreement was calculated when the same embryologists repeated the observations after a month's break. Inter- and intra-observer agreement was assessed using Fleiss' kappa coefficient and the intra-class correlation coefficient (ICC). The inter-observer agreement on the presence of CS (kappa: 0.477, 95% CI: 0.301-0.639) and their vesicles (kappa: 0.494, 95% CI: 0.345-0.643) was moderate, while the specific characteristics of CS assessment ranged from fair to moderate (kappa scores between: 0.157 and 0.563). The intra-observer agreement indicated an improvement on the level of agreement (kappa scores between: 0.162 and 0.795) compared to the inter-observer agreement. This study has shown a moderate level of inter- and intra-observer agreement when assessing day 5/6 human blastocysts for the presence of CS and their vesicles. When the specific characteristics of CS assessment occurred (such as the number of CS/vesicles) a slight to moderate level of agreement was seen among the embryologists. Agreement of specific characteristics of CS was not optimal, suggesting the need for further training using specifically designed CS quality assurance programme (QAP) modules, to determine if inter- and intra-observer agreement can be improved.