The fetal fraction of cell-free DNA in maternal plasma is not affected by a priori risk of fetal trisomy

Figures & data

Table I.  Fraction of fetal cfDNA values across risk categories.

Variable	n	Variable average value and range	Average fetal fraction (%) (SD)	p Value
Maternal age (MA)	High risk (HR) 214	42.9 years (42–50 years)	11.0 (4.6)	0.60
	Low risk (LR) 274	20.4 years (18–23 years)	10.7 (6.1)
Prenatal screening result (SC)	High risk (HR) 106	1 in 6 (1 in 3 to 1 in 10)	11.4 (6.0)	0.34
	Low risk (LR) 135	1 in 33,000 (1 in 6500 to 1 in 100,000)	10.8 (5.7)
Nuchal translucency measurement (NT)	High risk (HR) 91	5.2 mm (3.4–15.9 mm)	10.8 (4.0)	0.36
	Low risk (LR) 87	1.0 mm (0.1–1.2 mm)	11.4 (5.1)