KENNETH MOISE, JR.

Baylor College of Medicine, Houston, Texas

The procedure for intravenous entry into the fetal bloodstream is called by different names. The term PUBS, for percutaneous umbilical blood sampling, is commonly used in the United States; equivalent terms include cordocentesis and funipuncture. In PUBS, a needle guided by ultrasound is introduced into a blood vessel (usually the vein) of the umbilical cord to assess fetal status and treat fetal disease, particularly diseases of the blood.

PUBS was developed primarily in France, in the 1980s, to diagnose fetal toxoplasmosis, an infectious disease that can be transmitted by a pregnant woman to her fetus and can damage the fetal nervous system. Although relatively rare in the United States, toxoplasmosis is a common problem in France and elsewhere.

Between 1987 and 1991, an international registry monitored the applications of PUBS. Data collected from 7,000 procedures conducted in 11 centers showed PUBS being used most frequently to obtain chromosome diagnoses faster (within 48 hours) than is possible with amniocentesis (which requires weeks for results) in situations where delay might have serious clinical implications. In addition to toxoplasmosis, Rh disease, and nonimmune hydrops, PUBS has been used to diagnose fetal thrombocytopenia, a hemorrhaging condition caused by maternal autoimmune antibodies to platelets that cross the placenta, and to monitor drug levels and hyperthyroidism.

Therapeutically, PUBS has been indispensable in reversing hydrops in Rh disease. Data on 400 Rh fetuses transfused by PUBS, as reported at a 1989 PUBS conference, showed an 82 percent survival rate for hydropic fetuses. Survival rates vary from center to center, probably reflecting the severity of the cases handled. As PUBS is tried for reversing other conditions, varying degrees of success are being reported. Eight fetuses have been treated by means of PUBS for nonimmune hydrops caused by one of the recently identified agents, B19 parvovirus. All eight procedures resulted in the birth of healthy babies. In five attempts to correct chronic loss of blood between the fetus and its mother, only one transfusion was successful. Efforts to transfuse blood platelets into the fetus in cases of maternal-fetal platelet incompatibility proved impractical because platelets have a short half-life and multiple transfusions are required. Platelet transfusions performed near term, however, have averted the necessity for cesarean delivery.

Stem-cell transfusion is a new promising application of PUBS in which the cells that give rise to different classes of blood cells are transfused into fetuses with some type of blood cell disease. Of five stem-cell transfusions reported, three of the fetuses survived. One survivor had bare lymphocyte syndrome, a condition in which white blood cells fail to produce cell-surface molecules essential to immune response. Another had severe combined immunodeficiency (SCID). The third had beta thalassemia, an anemia widespread among people of Mediterranean origin, in which hemoglobin production is defective.

PUBS is not without risk. The PUBS registry's overall fetal fatality rate was around 1 percent. Other surveys have shown somewhat higher or lower rates. Survival is critically related to the particular disease and how far it has advanced; in fetal infection, mortality can be 11 percent, and in nonimmune hydrops as high as 31 percent. There is a risk of slowed heart rate, usually transient but more common if the umbilical artery is used, and of hemorrhage. In PUBS transfusions, there is the danger of the fetus moving and bumping into the needle, causing lacerations of the blood vessels. To prevent this, the fetus is often given drugs that induce temporary paralysis. When such risks are clearly explained to the mother, PUBS can be a very effective and lifesaving procedure. The risks, however, mitigate against the use of PUBS for prenatal screening when there are no indications of fetal illness.