A prenatal diagnostic test to detect genetic abnormalities and infection in the fetus. Percutaneous umbilical cord blood sampling (PUBS) is used after the 17th week of pregnancy and only when other diagnostic procedures have not provided a definitive result. Because it is a very complicated and difficult procedure, PUBS is performed exclusively by physicians who are specially trained in maternal-fetal medicine. Guided by ultrasound, the doctor uses a sterile needle to take blood from the fetus’s umbilical cord. PUBS is associated with more complications, such as injury to the umbilical cord, than other prenatal tests such as amniocentesis or chorionic villus sampling.