Challenging diagnoses of tetraploidy/diploidy and trisomy 12: utility of first-tier prenatal testing methods.

Chromosome mosaicism and low-grade mosaicism present a challenge for diagnosis in the era of SNP array and NGS. Tetraploidy is a rare numerical chromosomal abnormality characterized by the presence of four copies of each chromosome. The prevalence of tetraploidy/diploidy mosaicism cases is extremely rare in the human population.