Impact of maternal age on mosaicism rate in preimplantation embryos. A retrospective study

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Introduction Embryonic mosaicism is defined as the presence of multiple distinct cell lines within an embryo. Mosaicism is relatively common in preimplantation embryos derived from IVF and can be detected from trophectoderm (TE) biopsy provided we use a high resolution diagnostics platform (Ion Torrent). It is well known that advanced maternal age is linked to higher incidence of embryo aneuploidy. However, the relationship between mosaicism rate and maternal age is still unclear. Therefore, the purpose of this retrospective study is to investigate the relationship between mosaicism rate and maternal age in Alpha Fertility Centre, Malaysia from August 2017 to February 2018. Materials & Methods Four hundred and ten (410) patients (age range 18 – 47, mean age 30.7) underwent IVF cycles and their blastocysts were cultured to blastocyst stage. These patients were divided into 2 age groups, Group A (≤35 years, mean age 27.4) and Group B (>35 years, mean age 38.6). One thousand and two (1002) blastocysts from Group A and four hundred and twenty-nine (429) blastocysts from Group B with at least fair grade (Gardner, 1999) were biopsied respectively. Number of biopsy cells ranged from 2 to 10. All biopsied samples were subjected to preimplantation genetic screening (PGS) with next-generation sequencing (NGS). All samples were amplified and DNA libraries were constructed for sequencing using Ion TorrentTM PGM benchtop sequencer according to manufacturer's specifications (Ion Torrent, USA). The results were analysed by using ReproSeq Mosaic PGS w1.1 workflow (Ion Reporter Version 5.4). By following guidelines provided by Preimplantation Genetic Diagnosis International Society (PGDIS) 2016 , embryos with less than 20% aneuploidy in the TE sample were reported as euploid, over 80% aneuploidy were considered as aneuploidy and the remaining 20% to 80% aneuploidy were mosaic. Results Of the 1431 blastocysts assessed for ploidy status, 181 blastocysts were mosaic in Group A and 40 blastocysts were mosaic in Group B. Mosaicism rate for Group A was 18.1% (181/1002) and 9.3% (40/429) for Group B. The mosaicism rate for patients in Group B were significantly lower compared to patients in Group A (p=0.002). Conclusions Escudero et al, 2016 reported that mosaicism is independent of maternal age. However, our study shows that mosaicism rate is significantly higher in patients aged ≤35 years as compared to patient aged >35 years. Therefore, mosaicism rate might show correlation with maternal age. Nevertheless, further studies should be carried out to ascertain the relationship between maternal age and mosaicism rate.