Down syndrome: Earlier prenatal testing is recommended

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Down syndrome: Earlier prenatal testing is recommended

Question

I've heard about new guidelines for Down syndrome screening. What are the latest recommendations?

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Answer

A new study supports screening for Down syndrome in pregnancy weeks earlier than what has traditionally been recommended.

Blood tests — such as the quad screen or the maternal serum alpha-fetoprotein (MSAFP) test — have typically been offered around the 16th week of pregnancy to screen for Down syndrome, spina bifida and various other chromosomal disorders. These tests are still available. But the new study recommends other screening methods for Down syndrome earlier in pregnancy.

According to the study, the most effective screening is done in two steps between the 11th and 14th week of pregnancy:

  • Ultrasound. The doctor uses ultrasound to measure a specific region on the back of the neck of the fetus. This is known as a nuchal translucency screening test. Fetuses with abnormalities tend to accumulate more fluid in this tissue than usual.
  • Blood tests. Results of the ultrasound are paired with blood tests that measure levels of pregnancy-associated plasma protein A (PAPP-A) and a hormone known as human chorionic gonadotropin (HCG). Abnormal levels of PAPP-A and HCG may indicate a problem with the fetus.

When this two-step screening is done during the 11th week of pregnancy, researchers say it can identify 87 percent of babies with Down syndrome. By 13 weeks, accuracy of the two-step screening approach drops to 82 percent — about the same as traditional second-trimester blood tests.

If the screening tests are positive or worrisome or the risk of having a baby with Down syndrome is high, more invasive tests such as chorionic villus sampling or amniocentesis may be used to confirm the diagnosis.

About one in 20 women will have a false positive result with any of these screening tests — far more than those who have a baby with a chromosomal abnormality.

The decision to screen for Down syndrome or other abnormalities is personal. For many women, earlier screening will provide welcome peace of mind about their babies' health. For others, early news can offer precious time to prepare for the challenges that may lie ahead.

Last Updated: 11/15/2005
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