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Challenges behind prenatal exams

As prenatal exam choices grow, expectant parents are finding it harder to decide how to proceed

By Chelsea Conaboy
Globe Staff / March 19, 2012
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Parents expecting a child have a long list of decisions to make. For some, that list may be topped by one of the weightiest: Should they pursue prenatal testing to look for genetic abnormalities such as Down syndrome?

Many forgo testing. They may be at low risk for the conditions such tests commonly look for, or they may know that the results will not change how they feel about the pregnancy. Those who pursue it - either to decide whether to continue the pregnancy or to have all the information they can about their child - are able to know more today, earlier in pregnancy, than ever before.

Specialists say they expect that trend to continue, as new tests come on the market. But the growth of options and available information has made it more challenging to help parents decide which tests are right for them and translate the results, they say.

“We’re trying to walk that line between giving people information that is usable and useful and not scaring people half to death,’’ said Jennifer Hume, a genetic counselor at Newton-Wellesley Hospital.

Prenatal testing has changed considerably in the past decade. Amniocentesis, which uses a needle inserted through a woman’s belly to collect a sample of fluid from the sac that surrounds the fetus, has been widely used since the 1970s and was once the primary tool for assessing risk of Down syndrome and other chromosomal abnormalities. But that test can safely be performed only in the second trimester of pregnancy, after about 15 weeks.

Today, parents can get similar diagnostic information in the first trimester, by having chorionic villus sampling, or CVS, in which a doctor puts a needle through the abdomen or a small tube through the cervix to take a piece of the placenta for testing. CVS has become more widely available in recent years as specialists became trained in it.

Both amniocentesis and CVS can cause miscarriage, so doctors first screen women based on age, blood tests, or early ultrasound to evaluate their risk of having a child with a chromosomal disorder. But specialists say too many women, about 5 percent of all screened, test positive for a higher risk, meaning many with healthy babies are needlessly subjected to the small risk of miscarriage.

Screening tests introduced in recent months that analyze pieces of the fetus’s DNA floating in the mother’s bloodstream are making it possible to further hone in on who might be referred for the invasive tests.

A large study of one such test, Sequenom’s MaterniT21, by an independent group of researchers led by Women & Infants Hospital in Providence, found that the test detects 99 percent of all cases of Down syndrome when used in the high-risk group, while incorrectly returning a positive result in just 0.2 percent. The researchers projected that using the test to screen women with high-risk pregnancies could reduce the number of procedure-related miscarriages by as much as 96 percent.

That added certainty in screening requires a different conversation with parents, said Hume. She has begun offering the Sequenom test, which costs $1,933 for patients paying out of pocket and considerably less with insurance coverage, to those deemed at high risk. With traditional screening tests, most who are found to have an elevated risk of having a baby with Down syndrome still have a strong chance of having a healthy baby.

With the Sequenom test or others like it, Hume said, “if it’s positive, it’s probable that the baby does have Down syndrome.’’ Parents need to be prepared for that, she said.

When Christina Falcone, 29, of Arlington was pregnant with her second child, she and her husband debated whether to pursue testing. During her first pregnancy, blood tests showed she had an elevated risk of certain problems, but an amniocentesis found the baby to be healthy.

This time, “we just wanted to know,’’ Falcone said. “That way we were prepared.’’

When the blood tests showed an elevated risk again, Falcone chose the Sequenom test. It came back negative, and she opted not to have an amniocentesis to confirm it, trusting that their baby, due in June, will be healthy.

Dr. Susan Pauker, chief of the genetics program at Harvard Vanguard Medical Associates, said the age of information has changed prenatal testing.

Patients “want odds whittled down,’’ she said. “They want to know. They think they want to know. Then they learn that there is a problem, and they wish they didn’t know.’’

It’s her job to make them consider that possibility before they get to that point, she said, even as tests become more comprehensive..

The Counsyl Universal Genetic Test, which has been on the market for a couple of years, has made dozens of once-costly tests available through a single sample for about $350 per person for those patients paying out of pocket. The test evaluates whether parents are carriers of genes linked to conditions such as cystic fibrosis, Tay-Sachs disease, or sickle cell disease, as well as more rare conditions. (The company has been criticized for the test’s name; it does not evaluate all genes.)

And there is a growing discussion about whether to make more detailed genetic analysis widely available to parents. Microarray testing, which looks more closely at samples collected during amniocentesis or CVS, provides more information than the standard procedures, a recent study found.

Microarray testing can look so closely at a child’s genetic material that it can find missing or duplicate genes that have been linked to autism, schizophrenia, or heart defects.

“Most practicing physicians can’t keep up with the meaning of all this genetic material,’’ said Dr. Ron Wapner, lead investigator on the study and vice chairman for research at Columbia University Medical Center. “I can’t imagine how patients can do this.’’

It will be up to physicians and other health care providers to figure out how to manage the information collected, he said.

Hume, the Newton-Wellesley genetic counselor, said she wonders at what point more information becomes too much. Should she have children some day, she said, she isn’t sure which screening tests she would pursue.

“I think about those things,’’ she said. “And I want other people to think about them.’’

Chelsea Conaboy can be reached at cconaboy@boston.com. Follow her on Twitter @cconaboy.

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