title: Fetal cell-free DNA fraction estimation method based on based on difference in allele content between mother and fetus
design: Whole blood was centrifuged for 10 minutes at 1600g twice sequentially. After that plasma was separated and placed in new tubes, which were again centrifuged for 10 minutes at 1600g and then stored at 4˚C. Cell-free DNA was extracted from stored blood plasma using QIAamp DNA Circulating Nucleic Acid Kit (Qiagen) according to the manufacturer’s instructions. Samples underwent target amplification of highly polymorphic genome regions and then proceeded to standard preparation of sequencing libraries.