Sequenom, the San Diego-based developer of a prenatal genetic test for Down Syndrome, said today it has started a clinical trial of 10,000 pregnant women to compare its DNA blood test to the standard, more invasive tests of amniocentesis or chorionic villus sampling, in which doctors extract cells from the placenta. Sequenom (NASDAQ: [[ticker:SQNM]]) stock surged in September when it presented data showing its test was 100 percent accurate in a study of 400 women, although the stock has declined since on fears of competition from researchers at Stanford University. Investors expect results from about 1,000 patients by the end of the year, said Elemer Piros, an analyst with Rodman & Renshaw, in a note to clients today.