Percutaneous Umbilical Blood Sampling (PUBS) is the insertion of a needle through the mother's abdomen, like an amniocentesis, for the purpose of drawing a blood sample from the umbilical vein of the
umbilical cord. The most common reason for doing this is to get fetal blood for a rapid karyotype (chromosome analysis). Since amniocentesis fluid takes 7-14 days to get a result, there are situations (such as
an abnormal baby with signs of distress) in which it is helpful to know whether the baby has a fatal chromosomal defect, in which case the mother can be spared an emergent c-section for fetal distress.
Another reason for blood sampling is to manage Rh isoimmunization. If the baby is suspected to be anemic, blood sampling is the only way to confirm this, and also allows transfusion while the needle is in
place.
Below is an ultrasound photo of a blood sampling procedure. The needle can be seen as the white line coming in diagonally left-to-right from the upper left. The wavy lines in the center represent the umbilical
cord, where the tip of the needle is in the umbilical vein. The cord can be seen inserting into the placenta (the tissue at the bottom left of the screen). The black areas represent amniotic fluid. For orientation,
the top is the mother's skin, the bottom is the floor, the left is towards the mother's head, and the right is towards the mother's feet.