 The RNA study is an observational trial whose primary aim is to document the performance sensitivity and specificity of one or more laboratory developed test LDT using circulating cell-free fetal nucleic acids from maternal plasma to identify Down syndrome. Multiple test modalities are being pursued, including massively parallel sequencing and those utilizing differential methylation. The population being studied is women already having a diagnostic test e.g., amniocentesis, CVS between 10 weeks and 21 weeks 6 days gestation, and whose pregnancy is at high risk for having Down syndrome. The women provide informed consent. The karyotype will provide the gold standard against which the LDT test is judged. Samples and karyotypes will be collected from up to 25 prenatal diagnostic centers around the world and tested in several laboratories in the United States. The secondary aim is to develop a nucleic acid sample bank to allow documentation of subsequent improvements or new methodologies to identify fetal aneuploidy using circulating cell-free fetal nucleic acids. 