Views on Cordocentesis or Percutaneous Umbilical Blood Sampling (PUBS)

Written on August 21, 2007 by steven

With the continuing improvement in sonographic images, a method of inserting a long needle into the umbilical vein as early as week 17 of pregnancy has been developed. In percutaneous (Latin per = through; cutis = skin) umbilical blood sampling, or PUBS, a small volume of fetal blood is withdrawn, approximately 1 to 4 milliliters, or less than one­eighth of an ounce. This sample can be analyzed directly, without the need to grow cells in culture. This simplifies and speeds the diagnosis of some fetal abnormalities. The risk of PUBS or cordocentesis, also called funipuncture (Latin funis = cord), is estimated at about 1 to 3 percent, less than that of fetoscopy but greater than amniocentesis. This technique is performed under the

strictest sterile technique. Before the needle is inserted, the pregnant woman’s abdomen is cleansed with a sterile solution. As with amniocentesis, a local anesthetic may be injected

into the site where the needle will be inserted.

PUBS is always performed under ultrasonic guidance to localize the umbilical cord. Because there is some bleeding from the cord following the procedure, the ultrasound is continued after the needle is withdrawn to make sure the bleeding stops rapidly-which it usually does. The fetal heart is also monitored during and immediately following the procedure.

PUBS is performed only at specialized centers and is reserved for specialized circumstances. These might include -

• A woman seeking fetal diagnosis because of a high likelihood of a chromosomal or genetic abnormality, but requiring a very rapid assessment because her pregnancy is close to the legal limit for an abortion

• The need to diagnose certain blood disorders including sickle-cell anemia and hemophilia

• The need to diagnose certain metabolic disorders or fetal infection with organisms known to be teratogenic, including toxoplasmosis, rubella, cytomegalovirus, varicella (chicken pox), or parovirus B 19 (Fifth disease).

• Evaluation of Rh disease in the fetus as well as in utero treatment of Rh disease by blood transfusion

• The need to treat the fetus directly with drugs, for example, in fetal heart disease

• In later pregnancy to assess the fetal condition when there is intrauterine growth retardation or restriction

• In later pregnancy, to perform a rapid karyotype when there is fetal distress and a sonographically demonstrated major ab­normality; a karyotype may show the abnormality to be fatal and thus the mother is spared a cesarean delivery for a newborn that would not survive. Some obstetric experts believe that as physicians become more proficient in performing this technique, thus reducing its potential risks, PUBS will become more widely utilized.

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