A New Prenatal Blood Test for Down Syndrome

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.

Inclusion criteria

• Pregnant women between about 10 weeks and 21 weeks 6 days gestation who are undergoing a diagnostic procedure (i.e., chorionic villus sampling or amniocentesis) for karyotype analysis who have, on average, a high prevalence of Down syndrome (about 1:30 to 1:50).
• Three main sources are pregnancies screen positive for:

• the combined test at 10 to 13 weeks (NT, PAPP-A and hCG)
• the second trimester quadruple test at 15 to 18 weeks gestation
• integrated screening (PAPP-A and the quadruple test, with or without NT).
• Variations of the integrated test such as sequential testing will also be acceptable.
• Other, less common high risk groups would be women having diagnostic testing because of maternal age of 38 years or older at delivery, pregnancies with an abnormal ultrasound highly suggestive of a chromosome abnormality (e.g., major heart defect, clenched fist), and women with an inherited form of Down syndrome (Robertsonian translocation).

Exclusion criteria

• Nonpregnant women and women at relatively low risk for a Down syndrome baby.