Table 5.

Pretest Counseling – Comparison of Important Aspects between Sex Chromosome and Autosomal Aneuploidy

	Chance of a high-risk NIPT result	PPV	Maternal Condition	Mosaicism at CVS and true fetal aneuploidy	Phenotype of true positive	Prenatal diagnostic modality
SCA	0.3 – 0.6%	20 – 50%	Maternal unrecognized SCA = 6 – 24%	45,X - 16%	Majority undiagnosed during life Exception – 45,X - 70%	CVS- if NT > 3.0, or anomalies Amniocentesis – normal first trimester US
Autosomal aneuploidy	1.0 – 5.0%	Trisomy 21 - 50% (< 35 yo) - 80% (> 35 yo)	Maternal cancer = 1/1,800	T21 – 2% T18 – 4% T13 – 22%	Majority, if not all, diagnosed as a newborn	CVS or amniocentesis