Birth Defects Testing

Is a Birth Defect Test Accurate?

No test is 100% accurate. A screening test may be negative even when the baby has a birth defect. This is called a false-negative test result. It also is possible that a test will be positive—meaning the test result is abnormal—but the baby does not have the problem. This is called a false-positive test result. A screening test is considered positive when the results show that your chance of having a child with a birth defect is the same as, or higher than, that of a 35-year-old woman. When a screening test is positive, an amniocentesis will likely be recommended to find out for sure whether the baby has a problem.

Ultrasound accuracy has been reported to be:²

• 53% overall for finding birth defects.
• 90% for finding fatal defects.
• About 100% for some neural tube defects, such as anencephaly.

Amniocentesis has an accuracy of more than 99% for Down syndrome; CVS has similar accuracy.³

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Author:	Jan Nissl, RN, BS Sydney Youngerman-Cole, RN, BSN, RNC	Last Updated: October 12, 2006
Medical Review:	Renée M. Crichlow, MD - Family Medicine Adam Husney, MD - Family Medicine Siobhan M. Dolan, MD, MPH - Reproductive Genetics Renee H. Martin, PhD - Medical Genetics
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