DNA paternity testing, whether prenatal or post natal, is extremely accurate and will exclude the non-biological father with 100% accuracy. However, only the results of a post natal paternity test (if performed to legal requirements) will stand up in court.  Prenatal paternity testing results cannot be used in a court of law. Most courts will not suggest using prenatal testing to determine paternity and almost always wait until after the baby is born to verify paternity. One of the main reasons for this is to avoid encouraging the use of invasive procedures such as CVS that can put the unborn baby at risk.