Who: Offered to all pregnant women.

Why: To identify pregnancies at higher-than-average risk of certain serious birth defects, including neural tube defects, like spina bifida, and chromosomal abnormalities like Down syndrome.

When: First or second trimester.

How: Blood is taken from a woman’s arm. The laboratory measures levels of certain substances in the mother’s blood.

Risks: A little bruising or soreness at the needle site. Most abnormal test results are false alarms. Women with abnormal test results are usually offered further testing, such as ultrasound.

For more information, read the fact sheet Maternal Blood Screening for Birth Defects.

November 2008