"Prenatal testing to detect Down syndrome is carried out with amniocentesis or chorionic villus sampling. Both are invasive tests that carry about a  risk of miscarriage. Researchers said Tuesday however that they were developing a simple maternal blood test that can detect Down syndrome with a high rate of accuracy and greatly reduce the number of cases requiring an invasive test. Down syndrome occurs in about  in  births.  The new DNA sequencing technology relies on finding small bits of fetal DNA in the mothers blood something that has been difficult to do until now. In the study  pregnant women at high risk for having a baby with Down syndrome were tested.  Using the new technology researchers found they could rule out Down syndrome in  of cases sparing the women from further testing. The blood test did not produce false negative results showing the fetus did not have the disorder when in fact the condition was present.  Currently women in the United States are offered a blood test combined with an ultrasound test  called the combined test  to assess the risk of Down syndrome in pregnancy. The combined test still leaves an estimated  to  of women in need of invasive testing. The new blood test which is conducted in the first trimester could be used after the combined test or even as a firsttier test said the study authors from the Institute of Health Sciences in Hong Kong."