Using MRI to diagnose Down syndrome

What is Down syndrome?

The public’s understanding of Down syndrome has not kept up with advances in prenatal diagnosis and treatment of the condition, which has historically been met with trepidation. Since October is National Down Syndrome Month, this is a good time to reconsider what such a diagnosis means today.

Down syndrome was named after John Langdon Down, a 19th century British physician who carried out major research on the condition worldwide. According to the March of Dimes — an organization founded in 1938 to treat polio victims, which has since redirected its efforts to birth defects — Down syndrome is the most common genetic chromosomal disorder in the United States. Chromosomes are the structures that hold genes, which in turn store instructions for how the body works and grows.

The symptoms and their severity vary, and not everyone with Down syndrome has the same features. The most common signs include upward slanting eye lids, a flattened face and small head. Other effects include learning disabilities and developmental delays in children, along with other medical abnormalities later in life, which can include heart and gastrointestinal disorders.

About one in 700 babies (less than 1 percent) is born with Down syndrome. But with screening and diagnostic tests available today, conditions associated with the syndrome are revealed early, even before birth, letting health care providers and genetic counselors offer assistance and treatment both before and after delivery.

Thanks to prenatal screening, diagnostic testing and appropriate follow-up care, many born with Down syndrome today can expect to lead healthy, active lives at school, work and in society, some living 60 years or more. While Down syndrome is not preventable, there are risk factors that indicate the mother should be tested. These include a woman’s age and prior occurrences of the condition in her family.

Such are the benefits of early detection that the American College of Obstetricians and Gynecologists now recommends offering screening and diagnostic testing for all pregnant women. In some cases this even includes genetic counseling before becoming pregnant.

Prenatal screening and diagnostic testing

A health care professional or genetic counselor can offer a pregnant mother both prenatal screening and diagnostic testing and explain the pros and cons of the tests.

Screening tests can't determine with certainty whether a baby has Down syndrome, but they can show increased likelihood by looking for certain indicators. The process involves noninvasive blood tests and ultrasound of a specific area on the baby's neck. If these tests reveal a high risk for Down syndrome, a provider will then recommend diagnostic testing.

Diagnostic tests can more precisely identify whether a fetus has Down syndrome, although no test can be 100 percent either way. These tests include Chorionic villus sampling (CVS), where cells are taken from the placenta to look at fetal chromosomes.

In the other test, called amniocentesis, a needle is inserted into the uterus, a sample of the amniotic fluid is drawn and the chromosomes are studied. This test involves a slight risk of miscarriage.

Another test uses CT technology (computed tomography scan), which takes many X-rays at different angles to get ‘slices’ of the area of interest so the radiologist can look inside an organ without cutting it open. As CT scans involve radiation, there is some slight risk of damage to body cells which can lead to cancer. Some patients and families may therefore prefer another alternative: the MRI.

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How an MRI can diagnose Down syndrome

An emerging technology for prenatal diagnostic imaging is the MRI (Magnetic Resonant Imaging) test.

This is a widely used imaging system for getting very detailed images of tissues and organs in the body. It's different from X-rays and CT scans because there's no radiation involved. Instead, a magnetic field and radio waves energize the hydrogen atoms in the body, and with that, these atoms give off a signature that the MRI machine reads and translates into a digitized image.

Numerous studies have shown MRI is one of the safest technologies for imaging the body, according to GE Healthcare. The examination is painless, and the magnetic field produces no known tissue damage. These images provide physicians with valuable diagnostic information that lets them assess a patient’s condition.

There is, however, some concern by radiologists that Gadolinium, a contrasting agent used in MRI exams, may pose a threat to a pregnant woman. A recent study has argued that gadolinium dye could pose risks to a fetus and should best be avoided. An FDA Panel noted similar concerns when issuing a warning for the substance, which potentially required manufacturers to carry out further study.

GE Healthcare's guidelines recognize the potential for increased danger and recommend that MRI exams for pregnant patients should be carried out only if deemed essential in a risk-benefit analysis by the attending physician. This is determined on a case-by-case basis. If indicators are present, they will help parents make appropriate preparations, possibly including plans to give birth in a high-risk medical center where there are multiple levels of care available.

When it's determined to be both safe and ethical, early intervention can be a transforming prospect for those born with Down syndrome, offering a drastic upgrade in the potential quality of their lives. Every case and stage of life will have its own unique service and treatment needs. Much more information about Down syndrome is available through the National Down Syndrome Society.