Optimal timing of blastocyst vitrification after trophectoderm biopsy for preimplantation genetic screening

October Optimal timing of blastocyst vitrification after trophectoderm biopsy for preimplantation genetic screening Hsiu-Hui Chen 0 1 Chun-Chia Huang 0 1 En-Hui Cheng 0 1 Tsung-Hsien Lee 0 1 Lee- Feng Chien 1 Maw-Sheng Lee 0 1 ☯ These authors contributed equally to this work. 1 (MSL) 1 (LFC) 1 0 Division of Infertility, Lee Women's Hospital , Taichung, Taiwan , 2 Department of Life Sciences, College of Life Sciences, National Chung Hsing University , Taichung, Taiwan , 3 Institute of Medicine, Chung Shan Medical University , Taichung, Taiwan , 4 Department of Obstetrics and Gynecology, Chung Shan Medical University Hospital , Taichung, Taiwan , 5 Department of Obstetrics and Gynecology, College of Medicine, National Taiwan University , Taipei , Taiwan 1 Editor: Jo-Ann L. Stanton, University of Otago , NEW ZEALAND Is the timing of vitrification after trophectoderm (TE) biopsy associated with successful implantation and pregnancy after the embryo transfer of blastocysts subjected to preimplantation genetic screening (PGS)? In this retrospective cohort study, 1329 blastocysts from 223 patients were subjected to TE biopsy for performing array comparative genomic hybridization (CGH) tests. The PGS and frozen blastocyst transfer (FET) cycles were performed from December 2012 to May 2015. Only the good quality and expanded blastocysts on day 5 or 6 were selected for biopsy. After TE biopsy, the re-expansion grades relative to the original blastocoel were (1) collapsed blastocysts (CB), (2) 3/4 re-expansion but not full expansion (RE), and (3) full re-expansion or hatching (FE). All biopsied blastocysts were subjected to vitrification within 0.5±6 h after biopsy; the time intervals between TE biopsy and vitrification and the expansion grades at the time of vitrification were recorded. By combining two factors, namely the expansion grades and culture intervals between biopsy and vitrification, the patients were further divided into four groups, namely CB with a < 3 h culture interval (n = 34 cycles, Group I), RE and FE blastocysts with a < 3 h culture interval (n = 10 cycles, Group II); CB blastocysts with a 3 h culture interval (n = 6 cycles, Group III); and RE or FE blastocysts with a 3 h culture interval (n = 173 cycles, Group IV). The implantation (63.7%, 179/281) and clinical pregnancy (74.0%, 128/173) rates in Group IV were significantly higher than those in Group I (45.3%, 24/53; 50.0%, 17/34; P = 0.012 and 0.005, respectively). According to our findings, optimal vitrification timing > 3 hours to enable blastocysts to reach RE or FE provides improved implantation and pregnancy rates after FET. Trial registration: ClinicalTrials.gov NCT03065114 - Data Availability Statement: All relevant data are within the paper and supporting information files. Funding: The authors received no specific funding for this work. Competing interests: The authors have declared that no competing interests exist. Introduction The blastocyst stage is the optimal stage for performing biopsies for preimplantation genetic screening (PGS) [ 1 ]. The high efficiency of PGS at the blastocyst stage has being reported as a key factor determining the growing clinical application of this strategy worldwide [2±7]. For blastocyst biopsy, laser-assisted drilling is used to create a zona opening on day 3 or day 5 of development. The method of zona opening on day 3 allows some of the TE cells to herniate during blastocyst formation and expansion, which facilitates the biopsy process. However, this method may result in herniation of inner cell mass (ICM) cells instead of TE. In contrast, the method of zona opening on day 5 is performed at the expanded blastocyst stage with a hole drilled away from the ICM to ensure that only TE cells are biopsied. The disadvantage of this method is an obvious blastocyst collapse after TE biopsy. The collapsed blastocyst requires some time to seal the hole where the cells have been removed and reform the blastocoel [8± 10]. Biopsied blastocysts are routinely stored in liquid nitrogen for subsequent transfers. Blastocyst vitrification in the routine management of in vitro fertilization (IVF) cycles enables performing trophectoderm (TE) biopsy with high efficiency and minimal risks [ 3, 11, 12 ]. In past years, the clinical outcomes of PGS were focused on the biopsy stage to reduce embryo damage or technical risk (mosaic or allele dropout) [ 13 ]. However, the most appropriate time prior to vitrification following TE biopsy for PGS-FET remained unclear. The TE epithelium forms on the outside of blastocysts to act as a barrier and regulate the exchange and accumulation of small molecules and fluid during blastocoel formation [ 14 ]. TE biopsy typically alters the integrity of tight junctions (TJs) and causes morphological changes (blastocyst collapse and cells loss) because of decreased pressure. The TJs between TE cells are an essential component of the differentiated epithelial cells required for po (...truncated)