Fetal Blood Sampling

Fetal blood sampling, also called PUBS (Percutaneous umbilical blood sampling), is a procedure in which a small amount of blood is drawn from a fetus in-utero. The test is performed by an obstetrician or a trained perinatologist - maternal-fetal medicine specialists - in order to diagnose, treat and monitor fetal health problems during pregnancy.

How the Test is Done
Similar to an amniocentesis, the mother’s stomach is first cleaned with antiseptic. Using an ultrasound as guidance, a thin needle is inserted into a fetal blood vessel and a blood sample is removed. Medications or blood transfusions can also be given through the needle.

Fetal blood sampling is an outpatient procedure, but can sometimes take several hours to complete. There is some pain associated with fetal blood testing, but it should not last long or be more painful than a needle puncture to any other part of the body. When the procedure has been completed the mother will be required to rest in the hospital for several hours while the fetal heart rate is monitored.

When in Pregnancy is the Test Done?
Usually fetal blood sampling is done between weeks 20 and 23 of the pregnancy.

Who Should Have the Test
Pregnant women who have passed 20 weeks, have already had an ultrasound and amniocentesis, and have a high risk of a chromosomal disorder, or both parents are known carriers of a genetic disorder, should have a fetal blood sample taken. A sample should also be taken in cases where an ultrasound has shown fetal abnormalities.

Fetal blood sampling can also be used to diagnose and treat severe fetal anemia and other blood diseases, such as Rh Disease, to diagnose fetal infection, to check fetal blood oxygen levels, or to administer certain medications directly to the fetus. Of course, every pregnancy is different. If you feel that fetal blood sampling would be a good idea in your case, you should discuss it with your obstetrician.

Is the Test Mandatory?
No, fetal blood testing is not mandatory or routine. Pregnant women may ask to have their baby’s blood tested in-utero, or their doctor may suggest it to screen for genetic defects or anomalies, but no one should be forced to undergo the procedure if they do not wish to have it.

What the Test can Tell You
Fetal blood testing can reveal the presence of genetic or chromosomal defects, and the presence of abnormal cells in the fetus’ blood. It can also reveal the presence of certain diseases, often allowing for prenatal treatment. Fetal blood testing is the only way to test for fetal anemia.

What an Abnormal Result Means
The most common chromosomal disorder detected is Down Syndrome, which causes mental retardation and other health problems, such as heart defects. The test can also diagnose fetal infections, such as toxoplasmosis or rubella, blood diseases, fetal malformations, fetal platelet counts, and blood disorders such as fetal anemia and Rh disease, also known as isoimmunisation.

Pros, Cons and Risks
When preformed by an experienced medical profession, fetal blood sampling is a relatively safe, low risk procedure. There is, however, a two to five per cent risk of miscarriage following the test. Other risks include: bleeding from the needle wound, leaking of amniotic fluid, changes to the fetal heart rate and infections.

The benefits of fetal blood testing include allowing prenatal treatment for fetuses with severe blood damaging diseases. The test can also provide specialized information about the baby’s health that could not otherwise be known.

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