Does Laser-assisted Hatching Zona Thinning Improve The Pregnancy Outcomes Of Poor-quality Blastocysts In The Frozen-thawed Embryo Transfer Cycle?

Research question:Does laser-assisted hatching zona thinning improve the pregnancy outcomes of poor-quality blastocysts in the frozen-thawed embryo transfer cycle?Design:This was a retrospective study that included 230 women aged≤40 years who underwent frozen embryo transfer of poor-quality blastocysts（blastocyst scored<3BB）between January 1^st,2017 and October 1^st,2018 in a single reproductive medicine center.A total of 105 patients were in the assisted hatching（AH）group in which the zona of blastocysts was thinned by laser before transfer.125 patients were in the control group in which the blastocysts were non-manipulated.One to two poor-quality blastocysts were transferred according to patients’history,embryo quality as well as the mutual decisions of the physician and the patients.Results:All parameters in the patients’demographic characteristics and the cycle’s characteristics,including age,body mass index,duration of infertility,type of infertility,cause of infertility,basal hormone profile（follicle-stimulating hormone,luteinizing hormone,estrogen,progesterone,prolactin,testosterone and anti-Mullerian hormone）,endometrial thickness on the embryo transferring day,and the mean number of the embryo thawed,cryo-survived and transferred were not significantly different between the AH group and the control group.As for pregnancy outcomes,second trimester pregnancy loss was significantly higher in AH than in control group（4/47 vs 0/60,P=0.035）.Other pregnancy outcomes,including conception rate,implantation rate,clinical pregnancy rate,ectopic pregnancy rate,biochemical miscarriage rate,first trimester pregnancy loss,ongoing pregnancy rate and live birth rate were comparable between two groups.Odds ratio demonstrated no association between live birth and AH（Univariate,OR=0.787,CI 0.454-1.364,P=0.393;Multivariate,OR=0.652,CI0.351-1.210,P=0.175）.Conclusions:It seemed that zona thinning by laser was not supposed to perform on poor-quality,frozen-thawed blastocysts,since the pregnancy rates were not significantly different between two groups and conducting AH was not a contributing factor to live birth.The indications of AH were still needed to further investigate.