Abstract
Study question
Does laser use during trophectoderm biopsy affect biopsy results on prehatching embryos with regard to mosaicism ?
Summary answer
According to our findings laser usage during trophectoderm biopsy increases mosaic results on next generation sequencing (NGS) irrespective of embryo quality.
What is known already
Chromosomal mosaicism, which is a result of mitotic errors after fertilization, is defined as the presence of karyotypically distinct cell lines within an embryo. The introduction of NGS made it possible to detect chromosomal mosaicism at levels as low as 20%. The incidence of mosaicism is highly variable between clinics which reported the incidences between 4-32%. Apart from the biological reasons, there are also various technical factors that may impact the incidence of mosaicism. One of the most emphasized factors is the trophoectoderm biopsy technique. Laser usage and number of laser pulses may cause excessive heat during the procedure
Study design, size, duration
The mosaicism ratio in embryos in which trophectoderm biopsy was performed with or without laser, between January 2017 December 2020 in Istanbul Memorial Hospital (IMH) were examined retrospectively. A total of 13002 embryos were analyzed. A subgroup analysis was also performed regarding mosaicism ratios in different embryo qualities. Blastocysts were classified according to Gardner’s classification and classified as follows: top quality-TQ (4AA,5AA,6AA), good quality-GQ (3AA, 4,5,6AB,BA) and moderate quality-MQ (3,4,5 BB).
Participants/materials, setting, methods
The biopsy samples of the cases who had PGT-A in IMH between 2017-2020 were evaluated by NGS method. This method enables the identification of embryos with 20% to 80% mosaicism. The study assessed whether there was an increase in the embryos with mosaic results due to the use of laser during biopsy. The effects of laser use among the TQ (4AA,5AA,6AA), GQ (3AA, 4,5,6AB,BA) and MQ (3,4,5 BB) groups according to Garder classification were analyzed.
Main results and the role of chance
Trophectoderm biopsy was applied on 13002 embryos within the specified period. During biopsy in 5088 embryos laser was used and in 7843 embryos laser was not used, and biopsy was performed mechanically (flicking method). After observing the biopsy results, 945/5088 (18.5%) of the laser applied embryos; and 1087/7914 (13.7%) of laser not applied embryos were defined as mosaic(p < 0.0001). When mosaicism rates were examined according to embryo qualities, the rate of mosaicism was 19.3%(469/2430), 18.2%(290/1591) and 13.2%( 380/2875), 13.5 (426/3141) respectively in embryos with and without laser in TQ and GQ groups. A statistically high level of significance (p < 0.0001) was observed between the embryos evaluated as top quality and good quality before biopsy. Regarding the evaluation in the moderate group embryos, although the mosaicism rates tended to increase on the laser applied group side 40/248(16.1%), no statistical difference was observed when compared to non-laser group 103/670(15,4%). (P > 0.05)
Limitations, reasons for caution
The retrospective nature of the data is the main limitation of the study. On the other hand, the large number of NGS based PGT-A tested TQ and GQ embryos from a single center and resuts from single laboratory. However, further studies are required to corroborate our findings.
Wider implications of the findings
Laser dependent heat effect may increase mosaicism. To reduce the cell damage, teasing of cells should be avoided and a minimum number of laser pulses should be used in order to avoid excessive heat and contact points should be preferably confined to cell junctions
Trial registration number
None
Concordance of various chromosomal errors among different parts of the embryo and the value of re-biopsy in embryos with segmental aneuploidies