The nature of embryonic mosaicism across female age spectrum: an analysis of 21,345 preimplantation genetic testing for aneuploidy cycles

Is preimplantation genetic testing for aneuploidy (PGT-A) getting better? How can we know and how do we counsel our patients?

“…The other element in deciphering losses associated with PGT-A is the rate of so-called “mosaicism,” which represents intermediate copy numbers of individual chromosomes, and which confounds the interpretation of euploidy during PGT-A. Previous reports suggested that intermediate copy number rates were as high as 30% with average rates of approximately 15% ( 5 ). Furthermore, when PGT-A was first implemented, embryos with intermediate copy numbers were not transferred because of concerns about mosaicism in the conceptus.…”

The distribution of high and low-level mosaicism and maternal age: lessons and hesitations

“…In their study to determine how mosaicism varies across patient-specific variables and clinics, Armstrong et al. ( 3 ) demonstrated that mosaicism is overall higher in patients aged ≥35 years; however, the complexity of errors increases with advancing reproductive age. Although this latter finding complements previous data demonstrating similar trends in whole chromosomal aneuploidy, it is important to consider true signal vs. technical noise.…”

“…Although the study of Armstrong et al. ( 3 ) limits the performer of PGT-A to one single entity, further studies are needed to compare the accuracy of NGS mosaic calls across multiple independent laboratories that are responsible for their own validation.…”

“…Although the study by Armstrong et al. ( 3 ) adds to the body of knowledge surrounding the prevalence of mosaic embryos, a careful scrutinization of the data might lead one to ask if we should even care.…”

“…Biologic explanation regarding the nature of mosaicism starts with understanding where the prevalence lies. In light of Armstrong et al.’s ( 3 ) findings of higher complexity mosaicism with increasing maternal age, the question still lies of what is our threshold to use one of the embryos for transfer? Is there utility in rebiopsy before making that decision in cases of complex results, particularly in age groups where the availability of autologous embryos is limited?…”