P-265 The inner cell mass (ICM) hatching levels of blastocyst before vitrification associated with clinical pregnancy rates after single embryo transfer in PGT-A cycles
Authors: Lee M S , Chen H H , Huang C C , Chen C H , Lee C I , Lin P Y , Lee T H 
Published: June 2023

Abstract

Study question
Is there an association between ICM hatching levels and clinical pregnancy rate after single blastocyst transfer (SET) in preimplantation genetic testing for aneuploidy (PGT-A) cycles?

Summary answer
A blastocyst with ICM hatching level ≤ 50% has a better clinical pregnancy rate than that in a blastocyst with ICM hatching level &gt; 50%.

What is known already
The zona pellucida (ZP) breaching and trophectoderm (TE) herniating by laser assisted hatching before blastocyst stage is commonly used in blastocyst biopsy. The degree of hatching levels of ICM and TE is different between blastocysts before vitrification. However, completely hatched embryos may be more fragile due to the biopsy and vitrification/ warming processes and thus more susceptible to potential cellular damage prior to transfer. For the moment, no published studies have explored the entire set of information on morphological evaluation of biopsied blastocyst before vitrification including TE, ICM hatching levels, and clinical outcomes.

Study design, size, duration
A retrospective study including 578 PGT-A cycles with SET was conducted at Lee Women's Hospital between January 2020 and May 2022 (CS1-21156). The women age &lt;20 or &gt; 45 years were excluded in this study. The vitrification of expanded blastocysts on day 5 or day 6 was performed after TE biopsy. The hatching levels before vitrification were classified according the degree of TE or ICM hatching out from ZP.

Participants/materials, setting, methods
The groups of TE hatching levels were divided into (1) without hatching, (2) ≤25% hatching, (3) &gt;25% &lt;100% hatching and (4) hatching out. The groups of ICM hatching levels were divided into (1) ≤50% and (2) &gt;50% hatching. The primary outcome measure was the clinical pregnancy rate. Statistical analysis was performed using the generalized estimating equations (GEE), Spearman’s correlation, Kruskal-Wallis test, Fisher's exact test and c2 test.

Main results and the role of chance
The average of women age was 36.8 ± 4.4 (24-45) years. The overall clinical pregnancy, miscarriage and ongoing rates after SET were 65.4% (378/578), 10.3% (39/378) and 58.5% (338/578), respectively. Spearman's correlation analysis indicated that the TE hatching levels, the ICM hatching levels and the ICM grade were associated with the clinical pregnancy rate (p &lt; 0.01). According to multivariate regression analysis, the ICM hatching level ≤ 50% (OR: 1.863, 95% CI: 1.034-3.358, p = 0.038) and ICM grade A (OR: 1.662, 95% CI: 1.037-2.667, p = 0.035) were positively associated with clinical pregnancy probability. No significantly associations were found between women age, embryo day, TE hatching levels and clinical pregnancy rate (P &gt; 0.05) after multivariate regression analysis. The clinical pregnancy rate in the blastocyst with ≤ 50% hatching (68.7% (328/477) ) was significantly higher than that in the blastocyst with &gt; 50% hatching (49.5%, 50/101; p &lt; 0.001). Furthermore, the blastocyst with grade A and ≤ 50% hatching had a highest clinical pregnancy rate (76.9% (93/121)) and the blastocyst with grade B and &gt; 50% hatching had a lowest clinical pregnancy rate (46.3%, 38/82; p &lt; 0.001). The abortion rates between all groups were no significantly difference.

Limitations, reasons for caution
A smaller sample size in the group of ICM hatching &gt; 50% and further study with a larger sample size was needed to investigate putative impacts on clinical outcomes after SET.

Wider implications of the findings
These results demonstrate that a blastocyst with high degree of ICM herniating after biopsy and vitrification protocols decreased the clinical pregnancy probability. Selecting a biopsied blastocyst with either low ICM hatching level and grade A morphology for SET has a best pregnancy outcomes.

Trial registration number
not applicable