What will be the size of cell free fetal DNA, as it is smaller than maternal cell free DNA.

While looking on the NGS reads from cell-free DNA, how can we find the amount of fetal cell-free DNA present over there?

Is it depends on the median read length of the sequenced reads (like, as the overall median read length increases and thereby the cell-free fetal DNA length will also increase)

Seeking response.

Thanks in advance.