Fetal blood sampling is a procedure in which a small amount of blood is withdrawn from the fetus or the umbilical cord in order to perform diagnostic tests. The umbilical vein is the most common site the blood is obtained. This procedure, sometimes referred to as cordocentesis or percutaneous umbilical blood sampling (PUBS), is performed under direct ultrasound guidance using a 22-gauge amniocentesis needle.
Historically, the most common reason for fetal blood sampling was to determine if a fetus has severe anemia. Cordocentesis for this reason has waned over the past several years with the recent advent of noninvasive tests to assess for fetal anemia. Because the number of fetal blood sampling procedures has dropped considerably in recent years, patients are often referred to fetal treatment centers for this test.
The risk of losing the baby after this procedure is about 1%. In the case of a hydropic fetus, the risk of fetal loss may approach 7%. The cause of pregnancy loss may be due to infection (chorioamnionitis), rupture of membranes (bag of waters breaks), bleeding from the puncture site, or thrombosis (clot) of the vessel.