P-126 The KAT-Score is a useful indicator for predicting ongoing pregnancy in mosaic risk assessment in PGT-A: a prospective study with single vitrified-warmed blastocyst transfer
Authors: Harada Y , Fukunaga E , Maeda T , Ikeda M , Shiba R , Okano S , Kinutani M , Tanaka S , Shimada M , Sakuraba Y 
Published: June 2023

Study question

Does the mosaic risk score assessed by the KAT-Score correlate with clinical pregnancy and ongoing pregnancy?

Summary answer

A lower mosaic risk score assessed by the KAT-Score correlated with a higher ongoing pregnancy rate, but not with the clinical pregnancy rate.

What is known already

As the result of preimplantation genetic testing for aneuploidy (PGT-A), the result of analysis for mosaicism is obtained in addition to those for euploidy and aneuploidy. Viotti, et al. retrospectively analyzed 1000 mosaic embryo transfers, and showed that the rates of pregnancy and live birth differentiated stepwise depend on the type and level of mosaicism. Although it is possible to determine to the priority of embryo transfer according to the type of mosaicism, no prospective studies have been reported in which embryo transfer was performed using this method of selection.

Study design, size, duration

This is a prospective study conducted in a single IVF center between January 2020 and August 2022. A total of 104 single vitrified-warmed blastocyst transfer cycles were analyzed. The scoring of PGT-A embryos was assessed using the knowledge-based aneuploidy theoretical score (KAT-Score: Varinos Inc., Japan) in the range of 0 to 10. This study was approved by the Ethics Committee of the Institutional Review Board (IRB) of Kinutani Women’s Clinic, Hiroshima, Japan.

Participants/materials, setting, methods

The results of 104 vitrified-warmed single blastocyst transfers were classified into pregnancy (54 cycles) and non-pregnancy (50 cycles) groups. They were also classified into ongoing pregnancy (47 cycles) and non-ongoing pregnancy (57 cycles) groups. The correlations between KAT-Score and clinical pregnancy/ongoing pregnancy rates, were analyzed using the Wilcoxon signed-rank test and logistic regression analysis.

Main results and the role of chance

The KAT-Scores for 104 blastocysts ranged from 0 to 9. The distribution of scores is (KAT-Score 0: n = 43; 1-2: n = 21; 3-4: n = 4; 4-5: n = 16; 5-6: n = 7; 6-7: n = 5; 7-8: n = 6; 9: n = 2). First, mean values were compared between two different groups by use of the Wilcoxon signed-rank test. No significant difference in KAT-Score was observed between the pregnancy group and the non-pregnancy group (1.81 ± 2.42 vs. 2.78 ± 2.87; N.S.). On the other hand, the KAT-Score in the ongoing pregnancy group, was significantly lower than that in the non-ongoing pregnancy group (1.34 ± 1.98 vs. 3.04 ± 2.94; P &lt; 0.01). Second, binary logistic regression analysis was used to calculate the area under the curve (AUC) as a predictive measure of clinical pregnancy or ongoing pregnancy. The KAT-Score assessment of PGT-A embryos was a predictive indicator of ongoing pregnancy (AUC = 0.67: P &lt; 0.01), but not of clinical pregnancy (AUC = 0.59: N.S.). Multivariate logistic regression analysis, which included maternal age and morphological grade as confounding factors, showed that lower KAT-Scores correlated significantly with higher ongoing pregnancy rates (adjusted odds ratio: 0.77, 95% CI: 0.64−0.93, P &lt; 0.01). In addition, the ongoing pregnancy rate from embryo transfer with euploid or mosaic embryos was not affected by maternal age or morphological grade.

Limitations, reasons for caution

The main limitation of this study is small sample size. Further research is required to gain a more complete understanding of whether the KAT-Score is associated with pregnancy and ongoing pregnancy.

Wider implications of the findings

This study suggests that the KAT-Score may be used as one of the indicators to predict ongoing pregnancy regardless of maternal age and morphological grade. The scoring of 104 embryo transfers by KAT-Score provides statistically valid evidence for ranking mosaic embryos in the infertility clinic.

Trial registration number

not applicable