P-193 Does the day of laser-assisted hatching affects the clinical outcomes of single vitrified blastocyst transfer cycles? A propensity score–matched study
Authors: Huong T , Ha V  H , Nguyen Thi Lien H 
Published: July 2024

Abstract

Study question
What is the impact of different days of laser-assisted hatching on the clinical outcomes of single vitrified blastocyst transfer cycles?

Summary answer
Clinical pregnancy of single vitrified blastocyst were similar, irrespective of day of laser-assisted hatching.

What is known already
Assisted hatching aims to create a weakness in the ZP to aid embryo hatching and implantation. Day 5 assisted hatching is typically performed shortly before the embryo transfer while day 3 assisted hatching is performed before blastocyst culture expansion and vitrification. Despite over 25 years of use, there is still no standardized protocol for AH, and published data on its efficacy are controversial and inconclusive. While efforts have been made to study the link between AH techniques and pregnancy outcomes, there is limited consensus for optimizing AH protocols like the day of performance.

Study design, size, duration
This was a retrospective study based on data collected between January 2022 and October 2023. Propensity score matching (PSM) was performed in a 1:1 matching ratio. 123 patients of day 3 laser assisted hatching group (D3 LAH group) were successfully matched to 123 cycles of day 5 laser assisted hatching group (D5 LAH group). The D5 LAH group was from March 2023 to October 2023, and the D3 LAH from January 2022 to February 2023.

Participants/materials, setting, methods
Single vitrified day 5 embryo transfer, embryos survived after warming, and patient agreed to receive LAH were include in this study. We excluded donation cycles, missing data, severe female factors. Primary outcome is clinical pregnancy. Comparisons between groups were performed with chi-square test, Fisher’s exact test, Mann–Whitney U test, and Student’s t-test where appropriate, with a P value &lt;0.05 considered statistically significant. A multivariable analysis in the GEE model was adjusted for the confounding factors.

Main results and the role of chance
After propensity score matching, there was no significant difference in patient characteristics between the groups, creating similar cohorts. For example, the frequency of primary infertility was significantly different between groups initially (61% vs 46.7% in D5 LAH vs D3 LAH respectively, P = 0.004). Following propensity score matching the rate of primary infertility was similar in both groups (with SMD=0.08). Standardized mean difference (SMD) &lt; 0.1 suggests adequate variable balance after propensity matching. Clinical pregnancy rate were similar between two groups: 66/123 (53.7%) D3 LAH cycles and 75/123 (61%) D5 LAH cycles. When generalized estimating equation were performed: only TE grade, but not the day of laser assisted hatching, was noted to be an independent predictor of clinical pregnancy (OR = 0.068; 95% CI: 0.005-0.977; p = 0.048). Poor TE grade had a weak negative relationship with clinical pregnancy of single blastocyst cycles.

Limitations, reasons for caution
The main limitation of the study is its retrospective design and small sample size.

Wider implications of the findings
Clinical outcomes are comparable between day 3 laser assisted hatching and day 5 laser assisted hatching, although clinical pregnancy can be slightly improved with higher TE grade.

Trial registration number
not applicable