Blood Test Determines Fetus' Sex at 7 Weeks New testing technology is highly accurate, study finds By Rob Quinn, Newser Staff Posted Aug 10, 2011 4:30 AM CDT 0 comments Comments Expectant moms can know their baby's sex after just 7 weeks with new tests analyzing fetal DNA. (Shutterstock) (Newser) – Blood tests that promise to determine a baby's sex just seven weeks into pregnancy are highly accurate if used properly, a new study finds. Researchers found that the tests, which analyze fetal DNA in the mother's blood, are 95% accurate at seven weeks and 99% accurate at 20 weeks, the New York Times reports. Tests that analyzed urine instead of DNA, however, were accurate just 41% of the time—a prediction rate "worse than flipping a coin," a researcher tells LiveScience. The blood tests are sold online and in drug stores and are widely used in European hospitals—but not American ones. The technology to accurately predict the sex of the fetus so early on will help families worried about gender-linked diseases, experts say. But it raises fears that the tests will be widely used by parents wishing to choose the sex of their children, especially in China and India, where the boy-girl ratio is already greatly distorted because of sex-selective abortions.