- The Washington Times - Sunday, March 31, 2002

You should consider testing:

• If the mother is 35 or older.

• If the family has a history of chromosomal abnormality, neural tube defect or mental retardation.

• The parents are known carriers of a genetic condition that can be determined via prenatal genetic testing.

• The mother was exposed to a harmful chemical agent during pregnancy, as in chemotherapy.

• Maternal screening tests produced abnormal results.

Things to think about:

Discussing these questions with a doctor or genetic counselor can be helpful.

• How accurate are the test results?

• How often does my doctor perform the procedure?

• How concerned am I about the risk of miscarriage?

• Will this information change the way I will prepare for the birth of my baby?

• If a problem is discovered, what are my options?

The ABCs of prenatal testing

Here is a look at some of the most common prenatal tests:

Ultrasound

What is it? High-frequency sound waves are used to create pictures of what is going on inside the body.

What does it test for? It can reveal major structural abnormalities, including congenital heart defects.

How is it performed? Gel, which acts as a conductor for sound waves, is placed on the mother's abdomen. The doctor moves a small device called a transducer over the abdomen, directing sound waves into the uterus. The sound waves reflect off bones and tissue and are converted into black-and-white images.

How long does it take? About 20 minutes

When is it performed? Ultrasounds can be done at any point of the pregnancy.

How long does it take to get results? Results can be seen on the screen immediately.

What are risks? The exam is painless and poses no risks.

Are there any potential side effects? No.

Amniocentesis

What is it? Samples of amniotic fluid are removed using a needle and tested for genetic abnormalities in a lab.

What does it test for? Amniocentesis can detect chromosomal abnormalities, such as Down syndrome; genetic disorders, such as cystic fibrosis; and neural tube defects, such as spina bifida. It also can determine whether a baby's lungs are mature enough to breathe on their own.

How is it performed? An ultrasound is performed first to determine a safe site for the needle to enter. A long, hollow needle is inserted into the uterus. A small amount of amniotic fluid is taken from the amniotic sac, which surrounds the baby.

How long does it take? About half an hour.

When is it performed? Around 16 weeks gestation.

How long does it take to get results? About two weeks.

What are the risks? There is a chance of infection or miscarriage (about 1 in 200).

Are there any potential side effects? There is a chance the mother may experience cramping, fluid leakage or minor irritation around the entry site.

Chorionic villus sampling (CVS)

What is it? Samples of the cells that line the placenta, known as chorionic villi, are removed and tested for genetic abnormalities.

What does it test for? CVS can detect chromosomal abnormalities, such as Down syndrome, and genetic disorders, such as cystic fibrosis. Because no amniotic fluid is removed, it cannot test for neural tube defects such as spina bifida.

How is it performed? Guided by ultrasound, the doctor inserts a thin needle through the abdominal wall into the chorionic villi. A small sample of cells is then removed. The doctor alternately can get the cells by placing the tube through the woman's cervix.

How long does the procedure take? About 45 minutes

When is it performed? CVS typically is done between nine and 12 weeks gestation.

How long does it take to get results? Preliminary results usually come in two days; final results may take one week.

What are the risks? The risk of miscarriage because of CVS is about 1 in 150.

Are there any other potential side effects? The woman may experience infection, bleeding, cramping, fever or chills. Some studies have shown a possible relationship between CVS and limb malformation in the fetus.

Maternal blood screening

What is it? A blood test that measures levels of three substances in a woman's blood: alpha-fetoprotein (AFP), unconjugated estriol and human chorionic gonadotropin (HCG).

What does it test for? The blood work, combined with factors such as a woman's age, weight, race and pregnancy history, are calculated to determine whether a woman is at an increased risk of carrying a baby with a birth defect.

How is it performed? Blood is drawn from the woman at the doctor's office or at a lab.

How long does the procedure take? About 15 minutes.

When is it performed? The test most often is done between 16 and 18 weeks gestation.

How long does it take to get results? About one week.

What are the risks? A high number of women with abnormal results are found, upon further diagnostic testing, to have normal fetuses. Therefore, there is a risk of stress to the parents while undergoing more testing.

Are there any potential side effects? No.

Sources: Mayo Clinic; March of Dimes


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