Miscellaneous Prenatal Tests and Procedures
Not all the tests or procedures discussed here are performed in all pregnancies — only when a specific problem is present. When needed, they are usually performed in the second or third trimester. In fact, most of these tests are rarely done and are usually done in centers that specialize in fetal medicine. They may sound scary, but you should know what may be available if you develop a problem.
Fetal blood sampling
For fetal blood sampling — also known as PUBS(percutaneous umbilical blood sampling) or cordocentesis — a doctor withdraws fetal blood from the umbilical cord. This test lets your doctor obtain blood for rapid chromosomal diagnosis when time is critical, although testing cell-free fetal DNA in the mother’s blood can also be used in this situation.
Your doctor may perform this test in order to diagnose fetal infections, detect evidence of fetal anemia, or diagnose and treat a condition called nonimmune hydrops, in which fluid accumulates abnormally in the fetus. A maternal-fetal medicine specialist performs the procedure under ultrasound guidance.
The procedure is similar to an amniocentesis, except that the doctor directs the needle into the umbilical cord rather than into the amniotic fluid. Risks are low but include infection, rupture of the membranes, or fetal loss. (The risk of fetal loss is about 1 percent.)
Some fetuses develop anemia, which can be treated in utero (within the womb) with a blood transfusion directly into the umbilical cord. Conditions that may lead to anemia include certain infections (like parvovirus), genetic diseases, or certain blood group incompatibilities.
A fetal echocardiogram is basically a sonogram focused on the fetal heart. A maternal-fetal medicine specialist, a pediatric cardiologist, or a radiologist usually performs this procedure. You may need a fetal echo if you have a history of diabetes or a family history of congenital heart disease, or if an ultrasound shows any signs of a heart abnormality.
Sometimes your practitioner recommends a fetal echo if he sees any structural problem on ultrasound, because heart abnormalities are often associated with other birth defects.
Ultrasound can be used to perform Doppler studies of fetal and umbilical blood flow. These studies are a way of assessing blood flow to various organ systems and also within the placenta. A Doppler study is sometimes used as a test of well-being in fetuses with IUGR (intrauterine growth restriction).
MCA Dopplers measure the blood flow through a major blood vessel in the fetal brain and can detect fetuses that may be anemic from an infection or a blood group incompatibility.