Table 3.

Ratio of fetal/maternal DNA in maternal circulation

Weight of fetus/placental unita	Percentage fetal DNA in maternal plasma	Ratio of fetal to maternal DNA in maternal circulation	Whole fetal/cancer genome equivalents per 4 mL of plasmab	Number of malignant cells in tumor of this sizec	Likelihood of successful cancer detection
0.5 kg	10	1:10	1000	10 12	High
100 g	2	1:50	200	1011	High
10 g	0.2	1:500	20	1010	Moderate
1gd	0.02	1:5000	2	109	Low
100 mgd	0.002	1:50,000	< 1	108	Very low
10 mg	0.0002	1:500,000	< 1	107	Unlikely
1 mg	0.00002	1:5,000,000	< 1	106	Unlikely

^aBold numbers indicate experimental data

^b1 mL of blood contains approximately 2400 whole genome equivalents in pregnant women and normal individuals [40, 41]

^cCalculated by extrapolation of data mentioned by Uvili et al. [34]

^dThese ranges have been reported as thresholds for successful detection of cancer based on ctDNA by the most sensitive techniques available to date [29, 60, 61]