有一篇文件，研究了孕妇的孕周和体重对 胎儿游离DNA在母体cfDNA中占比的影响
文章名称：Gestational age and maternal weight effects on fetal cell-free DNA in maternal plasma
1、文章先统计所有孕妇的周期和体重分布
The study set included 22 384 maternal plasma samples drawn between 20 July 2012 and 31 December 2012 from women
with singleton pregnancies and a stated gestational age on the test requisition form of at least 10 weeks.
2、研究胎儿游离DNA的水平
a）与孕周关系
Maternal plasma cfDNA was isolated and analyzed by using the DANSRTM assay (Ariosa Diagnostics, San Jose, CA, USA),
which determines chromosome proportion and fetal cfDNA percentage simultaneously as previously described.
结果：The Harmony Prenatal Test determined fetal percentage via directed analysis ofcfDNA. Results
At 10 weeks 0 days to 10 weeks 6 days gestation,the medianpercent fetal cfDNA was 10.2%. Between 10 and.
21weeks gestation, percent fetalincreased 0.1% per week (p < 0.0001), and 2% of pregnancies were below 4% fetal cfDNA
b）与体重关系
结果：Table 1 shows the fraction of samples having at least 4% fetal cfDNA in relation to maternal weight.
The negative correlation between fetal cfDNA and maternal weight was statistically significant (p = 0.0003).