Prenatal diagnostic testing involves testing the fetus before birth (prenatally) to determine whether the fetus has certain abnormalities. Some of these tests, such as ultrasonography and certain blood tests, are often part of routine prenatal care.

Ultrasonography and blood tests are safe and sometimes help determine whether more invasive prenatal genetic tests are needed. Usually, these more invasive tests are done when there is an increased risk of having a baby with a genetic abnormality or a chromosomal abnormality. Below is a list of the diagnostic tests offered by our office.


Amniocentesis

This procedure involves a placing a very thin needle into the fluid filled sac (amniotic fluid space) that surrounds the baby. This is performed by a doctor under continuous ultrasound guidance. In this fluid are fetal cells that have fallen off the skin of the baby that are still alive. The genetic laboratory takes these cells and over time can determine if there are any chromosome abnormalities, such as Down Syndrome (also called trisomy 21) or trisomy 18 or trisomy 13.  In certain circumstances, detailed tests for single gene defects can also be performed. The fluid obtained from amniocentesis can also be tested for specific proteins looking for other birth defects such as spina bifida or abdominal wall abnormalities, etc.

Amniocentesis is most often offered for the following reasons:

  • Maternal age of 35 or older at the time of expected delivery
  • Fetal birth defects or anomalies seen on an ultrasound examination
  • An elevated risk for chromosome abnormalities from a first or second trimester screening test
  • Family history of genetic disorders that can pass from the parents to the baby, such as cystic fibrosis

The above listed reasons for amniocentesis mainly involve genetic testing. Other indications for this procedure may occur in a pregnancy such as performing tests on the amniotic fluid to see if the baby’s lungs are mature for delivery or to rule out an infection.

Amniocentesis is a common and very safe procedure, but there are some risks for the pregnancy and these will be discussed in more detail if this test is offered or suggested. The results of a genetic amniocentesis usually return in 6 to 10 days (and in certain cases a rapid preliminary test might be performed that can give some initial results within 2 to 4 days). Results from an amniocentesis for fetal lung maturity usually return within 1 to 2 hours.


Chorionic villus sampling (CVS)

This procedure involves placing a very thin catheter through the cervix to obtain a small amount of placental tissue (in some circumstances, this small piece of placenta might be obtained by placing a needle through the mother’s abdominal wall – similar to an amniocentesis). This test is also performed by a doctor under continuous ultrasound guidance. The genetic laboratory takes these placental cells and over time can determine if there are any chromosome abnormalities, such as Down Syndrome (also called trisomy 21) or trisomy 18 or trisomy 13.

 

CVS is most often offered for the following reasons:

  • Maternal age of 35 or older at the time of expected delivery
  • Fetal birth anomalies seen on an early ultrasound examination
  • An elevated risk for chromosome abnormalities from a first trimester screening test
  • Family history of genetic disorders that can pass from the parents to the baby, such as cystic fibrosis

CVS is a very safe procedure, but there are some risks for the pregnancy and these will be discussed in more detail if this test is offered or suggested. The results of a CVS usually return in 8 to 10 days.


Percutaneous umbilical blood sampling (PUBS) or cordocentesis

This procedure involves placing a very thin needle into the umbilical vein of the umbilical cord to obtain a small sample of fetal blood. PUBS is usually done when diagnostic information can not be obtained through amniocentesis, CVS, or ultrasound, or if the results of those tests were inconclusive. The procedure is similar to amniocentesis, except the objective is to retrieve blood directly from the fetus (via the umbilical cord) versus amniotic fluid. This test is performed by a doctor under continuous ultrasound guidance. PUBS is most often performed to evaluate whether the fetus is anemic or has some other blood disorder. It can also be used to evaluate for genetic abnormalities. There are risks for the pregnancy with PUBS and these will be discussed in more detail if this test is offered or suggested. The results of a PUBS usually return in 72 hours.