 The study will examine the sensitivity and specificity of a circulating cell-free nucleic acid test DNARNA to identify Down syndrome between about 10 weeks and 21 weeks 6 days gestation. In addition, the new test may be used to identify trisomy 13 and 18 as part of a more complete laboratory developed test. We hypothesize that the new circulating cell-free fetal NA-based test will accurately and precisely measure specific fetal markers in maternal circulation and that measurement will lead to the ability to noninvasively identify with high sensitivity and specificity, fetal chromosome abnormalities, such as Down syndrome. 