- The Washington Times - Sunday, March 31, 2002

From the time the pregnancy test turns positive, a pregnant woman receiving good prenatal care is bombarded with a menu of tests. AFP? CVS? Amniocentesis? Ultrasound?

If which tests to take seems confusing, figuring out what the tests can and cannot tell you is an additional maze to navigate.

"People need to understand what is available," says Vivian Weinblatt, a genetic counselor in Philadelphia and past president of the National Society of Genetic Counselors. "They need to understand what prenatal testing will tell them and then decide whether that is valuable information. We can't tell if a baby is perfect; we are not smart enough."

Diagnostic prenatal testing can find many conditions Down syndrome, spina bifida and other chromosomal abnormalities, for instance. Other tests, based on a woman's age and other factors, can tell whether she is at a statistically higher risk than others in her age group for carrying a child with a particular condition. Those tests are called screening tests, and many patients are not aware of the difference between the two, Ms. Weinblatt says.

One common screening test is the triple screen. Blood is drawn between the 15th and 20th week of the pregnancy, and levels of the chemicals alpha-fetoprotein (AFP), unconjugated estriol and human chorionic gonadotropin (HCG) are measured. By looking at the levels of these chemicals, doctors can tell if a woman is at increased risk of carrying a child with conditions such as Down syndrome or spina bifida.

If the results come back abnormal, doctors usually recommend further testing, such as a more in-depth ultrasound or amniocentesis, in which a small amount of amniotic fluid is drawn and analyzed for more definitive results.

However, expectant mothers should remember that many abnormal test results occur because of incorrect information supplied for the formula to calculate the result.

About 10 percent of women who take the triple screen will have abnormal results. Upon further testing, about 2 percent will be found to have a baby with defects, according to March of Dimes data.

It is important to remember that screening tests are looking for whether the odds are increased, Ms. Weinblatt says. They do not diagnose a condition.

"Even if you have a positive screen, the baby is probably normal," she says. "A test like that can tell you your risk for Down syndrome, such as 1 in 200 or 1 in 150. Even if the odds come in at 1 in 5, that leaves you a significant chance that the baby is OK."

Still, even knowing the odds are increased can be quite stressful. Lisa Gordon, a 35-year-old Fairfax mother of three, had elevated results in the triple screen during her first pregnancy five years ago. She and her husband worried a lot as they went through an amniocentesis, then worried more as they awaited those test results.

"For a whole week, we couldn't talk about it at all," Mrs. Gordon says. "A bunch of my friends have gone through the same thing. I was really scared."

To the couple's relief, further testing showed a perfectly healthy boy.

"It caused me a lot of worry," she says, "but I definitely wanted the tests done. I'd rather know than not know."

Many women may opt not to undergo prenatal testing. That is a personal decision, but they still should be given information about what is available, says Dr. John Larsen, professor of obstetrics, gynecology and genetics at George Washington University Medical Center.

"I call it making an offer," Dr. Larsen says. "The standard now in this country is if a woman is going to be 35 years old at the time of delivery, then it is standard to make her an offer of testing. She may then choose CVS (chorionic villus sampling) or amniocentesis, or she may choose to do nothing or do only a less invasive screening [such as ultrasound]. The vast, vast majority of women do something, at least an ultrasound. If it is done timely, it will pick up a large number of problems."

Age 35 is considered the gold standard in the United States because a woman's chances of carrying a child with a chromosomal defect increase with age. For example, a woman younger than 30 has a risk of less than 1 in 1,000 of conceiving a child with Down syndrome. A woman age 35 has a risk of 1 in 400. By age 40, that risk is 1 in 105, according to the National Institutes of Health.

Many women already in a higher-risk group because of age will opt to bypass screening testing and go right to diagnostic testing, Dr. Larsen says.

Ultrasound, in which high-frequency sound waves form images of the baby on a video monitor, can measure a baby's growth, evaluate movement, examine for malformations, even determine the baby's sex.

More invasive diagnostic tests include CVS and amniocentesis.

In CVS testing, a small sample of placental tissue (chorionic villi) is taken between 10 and 12 weeks and analyzed for chromosomal defects. Ultrasound helps determine the location of the fetus and the placenta; then a thin plastic tube is inserted either through the abdomen or through the vagina to obtain the sample. There is a risk of infection or miscarriage after the procedure, says Dr. Alfred Khoury, director of maternal-fetal medicine at Inova Fairfax Hospital.

The advantage to CVS testing is that it is done in the first trimester, Dr. Khoury says. Because CVS has a miscarriage rate of 1 in 150, Dr. Khoury often encourages his patients who opt for testing to go with amniocentesis, which is done later (at about 16 weeks) but can provide more information and carries a slightly lower risk (about 1 in 200) of miscarriage.

Dr. Khoury says women need to be aware of the risks in either procedure.

Amniocentesis, performed between 16 and 18 weeks, is performed by inserting a thin needle into the uterus via the woman's abdominal area. A small amount of amniotic fluid is withdrawn and analyzed.

"I don't recommend testing such as amnio for all women over 35," he says. "I recommend they be educated about the risks. There is a 1 in 200 chance of miscarriage with an amniocentesis. That is nothing to sneeze at. We are great consumers of technology but don't always think about the consequences."

Risks aside, amniocentesis can tell you a lot, Dr. Khoury says. If a woman comes in with a high AFP result (indicating spina bifida), the test can definitively tell if the baby has that condition. The test can count the number of chromosomes (which can definitively tell Down syndrome and several other chromosomal abnormalities). If there is a family history of such conditions as sickle cell anemia, Tay Sachs disease or cystic fibrosis, doctors can do special testing to look for those disorders, as well.

"I never say, 'Everything is fine,'" Dr. Khoury says. "If the chromosomes are normal, I say they are normal. If the exam shows no abnormalities, I say there are no abnormalities. What people need to understand is that for all our knowledge, we are still very ignorant."

The future of testing

Better first-trimester screening is available and eventually may replace some later screening tests, doctors say.

They are now able to combine a certain ultrasound measurement (called a nuchal translucency) and blood tests in the first trimester to pick up cases of Down syndrome with 90 percent accuracy and a false positive rate of 5 percent, Dr. Khoury says.

In the nuchal translucency test, which is done between 11 and 13 weeks, ultrasound is used to measure precisely the amount of fluid in a small space behind the baby's neck. If a baby has a chromosomal disorder, the amount of fluid may be increased. The ultrasound result is combined with blood tests that measure pregnancy-associated plasma protein (Papp-A) and the chemical free-beta HCG.

The nuchal translucency and blood work combine to make a screening test. It measures a woman's statistical chances of having a baby with chromosomal abnormalities, Dr. Khoury says. If the results come back as suspicious, the woman will be referred for CVS or amniocentesis for more definitive results.

However, the high accuracy rate of the nuchal translucency means that fewer women will have to undergo the risker and more invasive tests, Ms. Weinblatt says.

"There is a lot of potential to first-trimester screening," she says. "I really do think there is a huge benefit to doing these tests early, especially for those patients who can be satisfied with less than 99.9 percent accuracy. For patients who have tried a long time to get pregnant, they may be more inclined to find a less invasive way to test and decrease their chance of miscarriage."

Some clinics have taken the nuchal translucency a step farther. The integrated test, which has been tested and popularized in England, combines the nuchal translucency with quadruple-screen results (AFP, estriol, HCG and the protein dimeric inhibin-A) in the second trimester. The combined data can detect the likelihood of Down syndrome 85 percent of the time with only a 1 percent false positive rate, says Dr. Nicholas Wald, a British researcher who wrote a study published in the New England Journal of Medicine in 1999.

In the study, Dr. Wald looked at the blood work and nuchal translucencies of nearly 100,000 women.

The current false-positive rate for the triple screen alone is 5 percent, Dr. Wald points out in his study. He is referring to the rate to determine the risk for Down syndrome specifically.

Integrated testing ideally will reduce the number of amniocentesis referalls, says Dr. Arthur Zebelman, director of clinical operations for Seattle's Dynacare laboratories, one of the companies that does integrated testing in the United States.

"The most frustrating and scary thing about [current screening procedures] is that the majority of women referred for further testing do not, in fact, have a Down syndrome child," Dr. Zebelman says.

"I would be hard-pressed to say there is a tremendous economic benefit to integrated testing, but if you can put a cost on concern of expectant parents, then that is significant," he says. "A 1 percent rate of false positives is a lot less than 5 percent. There is some risk of miscarriage with amniocentesis and CVS, so a lot of couples want to avoid having them."

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