Triple Threat Blood Test for Moms-to-be

DNA blood test detects Down syndrome and two other chromosome disorders in first trimester

/ Author:  / Reviewed by: Chris Galloway, M.D.

(RxWiki News) A recently available blood test already known to detect Down syndrome in unborn babies can also detect two other serious chromosomal disorders as early as ten weeks into the pregnancy.

Research investigating 1,702 normal pregnancies and 286 pregnancies with a chromosomal disorder has shown that the test can also identify trisomy 18 (called Edwards syndrome) and trisomy 13 (Patau syndrome).

"Ask your OB/GYN which diagnostic test is right for your pregnancy."

Adding to research published last October about the DNA test's ability to test for Down syndrome, this larger,international study was led by Glenn Palomaki, PhD, and Jacob Canick, PhD.

Both are from the Division of Medical Screening and Special Testing in the Department of Pathology and Laboratory Medicine at Women and Infants Hospital of Rhode Island and The Warren Alpert Medical School at Brown University.

The test correctly identified 100 percent of the 59 pregnancies with trisomy 18 as having the disorder. It tested positive for all but one of the 12 pregnancies with trisomy 13.

The test gave false positives for trisomy 18 in less than half a percent (0.28) of the pregnancies and in about 1 percent of the cases for trisomy 13.

Three women with trisomy 18 were among the 17 for whom the test was inconclusive.

Up to 70 percent of fetuses with trisomy 18 will die before birth, and only about half of those who make it to full term survive their first week of life.

Survival rate past the first year for trisomy 18 is about 5 percent, and the children have significant medical and developmental problems.

Trisomy 13 is just as serious but about half as common as trisomy 18.

The blood test could be offered to women in high risk groups for giving birth to a child with Down, Edwards or Patau syndromes, such as women over age 35.

No information was provided regarding the cost of the test or when it might be available for women.

Previously, the most accurate ways to test for these disorders involved more invasive testing, such as withdrawing amniotic fluid from the womb during an amniocentesis. But these procedures carry risks to the baby.

The Centers for Disease Control and Prevention (CDC) published in 1995 that about one of every 200 invasive diagnostic procedures will lead to a miscarriage.

"Having access to such a comprehensive, DNA-based test that can be done early in pregnancy will give us more information so that we can better guide which patients should consider diagnostic testing," said Dr. Barbara O'Brien, who oversaw the study at one of the 27 prenatal diagnostic centers involved in the research.

The study appeared online February 2 in the journal Genetics in Medicine.

The study was funded by industry, but specific companies were unavailable. Information on possible conflicts of interests of the authors was unavailable.

Reviewed by: 
Review Date: 
February 4, 2012
Last Updated:
February 5, 2012