Diagnostic Tests

Some prenatal tests are screening tests and only reveal the possibility of a problem. Other prenatal tests are diagnostic, which means they can determine — with a fair degree of certainty — whether a fetus has a specific problem.

The following diagnostic tests are performed at the Maternal and Fetal Specialty Center. You may have one or more of the following tests performed based on your condition, risk factors and indicators, or screening results.

Chorionic villus sampling (CVS)

Chorionic villus sampling involves removing a small amount of tissue from the placenta between 11-13 weeks. The doctor removes this tissue either by going through the mother’s abdomen with a thin needle, or through the cervix with a thin tube. Ultrasound is used to help guide the doctor during the procedure.

CVS is used to test for evidence of chromosomal abnormalities in the fetus, such as Down symdrome. CVS is an alternative to amniocentesis. The advantage of CVS over amniocentesis is that a CVS test can be performed earlier, allowing more time for you to receive counseling and make decisions. Risk of miscarriage, although small, is higher with CVS than with amniocentesis and must be weighed against any benefits.

Amniocentesis

Amniocentesis involves removing a small amount of amniotic fluid (water that surrounds the baby). The doctor uses ultrasound to help guide a thin needle through the mother’s abdomen to get this fluid. This test is done after 15 ½ weeks.

Amniocentesis is most often used to detect Down syndrome and other chromosomal abnormalities, spina bifida, anencephaly, and inherited metabolic disorders.

Fetal echocardiogram

A fetal echocardiogram is used to check for problems in a baby’s heart structure or heart rhythm. This test provides early detection of congenital heart defects. A fetal echocardiogram is a level II ultrasound test and is painless and noninvasive. Fetal echocardiograms are usually performed in the second trimester of pregnancy, at about 18 weeks.

Situations in which a fetal echocardiogram may be necessary include:

• If a sibling was born with a congenital heart defect
• You have a family history of congenital heart disease
• A chromosomal or genetic abnormality is discovered in the fetus
• If you have taken certain medications that may cause congenital heart defects
• If you have abused alcohol or drugs during pregnancy
• If you have diabetes, phenylketonuria, or a connective tissue disease
• If you had rubella during pregnancy
• Prenatal ultrasound has discovered possible heart abnormalities

Nonstress test

A nonstress test (NST) can determine if your baby is responding normally to stimulus. A nonstress test is used mostly in high-risk pregnancies or when a health-care provider is uncertain of fetal movement. A nonstress test is performed at any point in the pregnancy after 26-28 weeks when fetal heart rate can appropriately respond by accelerating or decelerating.

Ultrasound

Ultrasound tests are routinely performed throughout pregnancy. For high-risk patients ultrasound tests can be targeted to look at specific aspects of the fetus based on results of prenatal screening or previous ultrasounds.

• Nuchal translucency ultrasound – a nuchal translucency ultrasound helps assess your baby’s risk of having Down syndrome or other chromosomal abnormalities as well as major heart problems. A nuchal translucency ultrasound measures the clear space in the tissue at the back or your baby’s neck. Babies with abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, causing this clear space to be larger than average.
• Marker and detail ultrasound – A marker and detail ultrasound is performed to look for specific conditions in the fetus that are known to be related to chromosomal abnormalities. A marker is a slight deviation from the normal anatomy. Markers may or may not indicate a problem. An amniocentesis or CVS would be used for further diagnosis and to confirm chromosomal abnormalities.
• Growth ultrasound – Growth ultrasounds are used to make sure your baby is growing on target.
• AFI ultrasound – an AFI ultrasound is used to measure the amount of fluid surrounding your baby. Amniotic fluid protects your baby and aids in development. An AFI ultrasound is used to identify abnormal amniotic fluid levels which could lead to birth defects or pregnancy complications.