P-757 Clinical and neonatal outcome of single vitrified-warmed blastocyst transfer with complete zona pellucida removal using laser-assisted hatching
Authors: Baatarsuren M , Sengebaljir D , Ganbaatar C , Erdenekhuyag B , Tserendorj T , Amarsaikhan A , Dorjpurev A , Ganbat G , Boris T , Khangarid A , Jamiyansuren J 
Published: June 2022

Abstract

Study question
Complete zona pellucida (ZP) removal using laser assisted hatching can improve clinical and neonatal outcome in single vitrified-warmed blastocyst transfer (SVBT) cycle?

Summary answer
Implantation rate, clinical pregnancy rate and live birth rate can be improved by complete removal of zona pellucida, whereas no impact on neonatal outcomes.

What is known already
Assisted hatching (AH) technique widely used in assisted reproductive technology for improving clinical outcome in frozen embryo transfer (FET), which could impair successful embryo hatching out of the zona pellucida (ZP) due to ZP hardening during vitrification-warming. The zona thinning and drilling methods of AH doesn’t affect clinical, live births outcomes and it could increase monozygotic twin birth, risk of placenta associated diseases. But recent studies showed that the complete removal of ZP may increase the chance of blastocyst adhesion and outgrowth afterwards, which required to be proven.

Study design, size, duration
Retrospective study data collected from July 2015 to November 2019 included SVBT in the Ojinmed IVF center. We divided into 2 groups as follows: case group 160 (randomly selected complete removal of ZP) and control group 160. The clinical outcomes were implantation rate (IR), clinical pregnancy rate (CPR), live birth rate (LBR), miscarriage and neonatal outcomes including monozygotic twin, birth baby sex, birth weight, height and gestational weeks. All parameters were compared between two groups.

Participants/materials, setting, methods
320 vitrified blastocyst transfer cycles in 215 patients underwent a clomiphene-based minimal ovarian stimulation protocol or drug-free natural cycles. All embryos were vitrified-warmed by Cryotop method (Kitazato, Japan). Complete removal of ZP selected an survived blastocysts after warming and used an immediate laser drilling (Laser: 1.8-2.2 ms, Octax NaviLaseTM) in perivitelline space. And gently glass pipetting done for complete removal of ZP. Statistical analysis performed by Chi-square test and logistic regression analysis using STATA 12.

Main results and the role of chance
A total 320 SVBT cycles, including ZP completely removed 160 cycles and control 160 cycles. In analysis of the patient's age, fertility causes and fertilization methods were not significant (p &lt; 0.05) between two groups. The IR (55.2 % and 66.2 %, p &lt; 0.01), CPR (39.3 % and 52.5 %, p = 0.01) and LBR (29.3 % and 43.7 %, p &lt; 0.01) are highly correlated between the control and the completely removal of ZP group, respectively. In multivariable logistic regression analysis showed the completely removal of ZP group had significance for IR (aOR 0.54, CI 95 % 0.31-0.93, p = 0.02), CPR (aOR 0.56, CI 95 % 0.32-0.96, p = 0.03) and LBR (aOR 0.56, CI 95 % 0.32-0.99, p = 0.048), which adjusted by patient age, blastocyst grade and vitrification day. Miscarriage rate didn’t show significance (23.8% and 21.4%, p = 0.73) between groups. The neonatal outcomes including monozygotic twin, sex of the births, average gestation week and birthweight were non significant (p &lt; 0.05) between two groups (49 for control group and 66 for case group) children.

Limitations, reasons for caution
The result of the current retrospective study is limited to data from a single IVF center.

Wider implications of the findings
Our study suggests that complete removal of ZP using laser assisted can improve clinical outcomes including implantation, clinical pregnancy and live birth after SVBT. And it may doesn’t affect to miscarriage rate and neonatal outcome.

Trial registration number
not applicable