Down syndrome -- screening and tests during pregnancy

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by Julie Snyder

DNA testingJust a few years ago, most of women carrying a child with Down syndrome didn't learn the news until delivery. The screening tests may have given false assurance or the moms might have opted out of diagnostic testing.

One in every 691 babies in the United States -- or around 5,500 each year -- is born with Down syndrome. It's the most common genetic condition in the United States, occurring in all socio-economic levels and in people of all races. More than 400,000 people live with Down syndrome in the United States.

Screening and tests

First trimester screen

Currently, risk factors, sonography, and maternal serum markers combine to estimate a woman's risk of carrying a baby with Down syndrome.

Between 11 and 13 weeks of pregnancy, you'll be offered a blood test and nuchal scan to screen for chromosomal abnormalities. Levels of the protein PAPP-A and the hormone, hCG, as well as maternal risk factors and your baby's ultrasound measurement determine an overall risk factor.

With the first trimester screening test, about 5 percent of normal pregnancies will have an abnormal result, but only about 2 to 3 percent of the women whose results show an increased risk will actually have a baby with a chromosome abnormality.

A positive result on this screen means that there is a 1 in 100 to 1 in 300 chance that the fetus has an abnormality.

Second trimester screening

Between 15 and 18 weeks, you may be offered another screening test, the AFP3. This test, sometimes called DownScreen Plus, or a multiple marker test, helps identify the risk that your baby has a possible neural tube defects or chromosomal problems such as Down syndrome.

Diagnostic tests

If your screening results indicate an increased of carrying a baby with Down syndrome, your doctor may suggest diagnostic testing using invasive methods such as amniocentesis and chorionic villus sampling.

These procedures are not entirely without risk. 1 in 100 women who undergo CV sampling have a miscarriage. Amniocentesis results in a pregnancy loss every 1 in 400 to 1 in 200 tests.

It's all in the blood -- mom's that is!

What if you could just have a bit more blood drawn around 10 weeks and learn if your baby has Down syndrome and other chromosomal abnormalities?

You could. A new type of test offers results several weeks sooner than those already in use. Studies indicate it gives fewer false positives, especially in women at high risk of carrying offspring with Down syndrome.

Circulating fetal DNA testing for Down syndrome

These new tests examine fragments of fetal DNA circulating in the mother's blood. They promise powerful tools for gleaning information about your unborn offspring.

They may soon create another option for prenatal diagnosis of Down syndrome and other chromosomal abnormalities and become a routine part of prenatal care. Observers expect the advantages of the non-invasive tests to expand the pool of women who opt for prenatal genetic screening in the United States each year from fewer than 100,000 to as many as 3 million.

Costs and ethics

As of June 2012, $235 out-of-pocket for women with private insurance and $1,900 for women without insurance.

Sequenom licensed the method for non-invasive prenatal diagnosis in 2005. Since then a tangle of lawsuits, complaints, warnings, and newly released tests have appeared.

Mildred Cho, a bioethicist at the Stanford University School of Medicine in California believes that if a single company has a monopoly on the market, they will be able to dictate the standard and quality of care.

A monopoly could potentially pushing costs out of reach for government programs such as Medicaid, which covers as many as 60 percent of the births in some states. Many potential parents would be affected.

Making a choice

When you learn that your child has Down syndrome, you face difficult choices. The diagnosis allows you to:

✓ Begin planning for a child with special needs
✓ Address anticipated lifestyle changes
✓ Identify support groups and resources
✓ Make a decision about carrying the child to term

An estimated 92 percent of all women who receive a prenatal diagnosis of Down syndrome choose to terminate their pregnancies, according to research reviewed by Dr. Brian Skotko, a pediatric geneticist at Children's Hospital Boston.

Dr. Skotko is concerned that parents may receive outdated or inaccurate information. One program that helps educate families is "First Call," offered by the The Down Syndrome Association. It distributes information to OB/GYN and perinatology practices and has volunteers available to talk with expectant and new parents, if requested.

Would you opt for a noninvasive Down syndrome prenatal test like MaterniT21 PLUS?

Photo courtesy of iStockphoto.