Clinical application of noninvasive chromosomal screening for elective single-blastocyst transfer in frozen-thawed cycles

Background: The objective of this study was to explore the clinical application of noninvasive chromosomal screening (NICS) for elective single-blastocyst transfer (eSBT) in frozen-thawed cycles. Methods: This study retrospectively analysed the data of 212 frozen-thawed single-blastocyst transfers performed in our centre from January 2019 to July 2019. The frozen embryos were selected based on morphological grades and placed in preincubation for 6 h after warming. Then spent microdroplet culture media of frozen-thawed blastocysts were harvested and subjected to NICS. The clinical outcomes were evaluated and further stratified analysis were performed, especially different fertilization approaches. Results: The clinical pregnancy, ongoing pregnancy, and live birth rates in the euploidy group were significantly higher than those in the aneuploidy group (56.2% versus 29.4%) but were nonsignificantly different from those in the chaotic abnormal/NA embryos group (56.2% versus 60.4%). Compared with day6 (D6) blastocysts, D5 blastocysts had a nonsignificantly different euploidy rate (40.4% versus 48.1%, P = 0.320) but significantly increased clinical pregnancy (57.7% versus 22.2%, P < 0.001), ongoing pregnancy (48.1% versus 14.8%, P < 0.001), and live birth rates (48.1% versus 13.0%, P < 0.001). The percentage of chaotic abnormal/NA embryos group was significantly higher among D5 embryos than among D6 embryos (30.1% versus 11.1%, P = 0.006). The percentage of aneuploid embryos was higher among the embryos with lower morphological quality(21.5% among ‘good’ embryos versus 34.6% among ‘fair’ embryos versus 46.0% among ‘poor’ embryos, P = 0.013); correspondingly, the overall clinical pregnancy, ongoing pregnancy and live birth rate rates showed similar declines. Conclusions: NICS combined with morphological assessment is an effective tool to guide frozen-thawed SBT. The optimal embryo for SBT is a ‘euploid embryo with good morphology’, followed sequentially by a ‘chaotic abnormal/NA embryo with good morphology’, ‘euploid embryo with fair morphology’, and ‘chaotic abnormal/NA embryo with fair morphology’.