Are women over age 35 at increased risk of having a baby with a birth defect?
A woman’s risk of having a baby with certain birth defects involving chromosomes (the structures in cells that contain genes) increases with age. Down syndrome is the most common chromosomal birth defect. Affected children have varying degrees of mental retardation and physical birth defects. A woman’s risk of having a baby with Down syndrome is (1):

At age 25, 1 in 1,250
At age 30, 1 in 1,000
At age 35, 1 in 400
At age 40, 1 in 100
At 45, 1 in 30
At 49, a 1 in 10

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women, regardless of age, be offered a screening test for Down syndrome and certain other chromosomal birth defects (6). Screening tests are blood tests done in the first or second trimester, sometimes with a special ultrasound. They help evaluate a woman’s risk for having a baby with certain birth defects, but they cannot diagnose a birth defect.

ACOG also recommends that all pregnant women have the option of choosing a diagnostic test, such as amniocentesis or chorionic villus sampling (CVS), instead of a screening test (6). A diagnostic test can tell if a person does or does not have a certain condition. Amniocentesis and CVS are highly accurate in diagnosing or ruling out a birth defect, but these tests may pose a very small risk of miscarriage.

Until recently, providers routinely offered diagnostic tests, rather then screening tests, to women over age 35 because they have increased risk of having a baby with chromosomal birth defects. However, ACOG now recommends that providers offer women over age 35 the option of having a screening test to evaluate their risk before deciding whether or not to go ahead with amniocentesis or CVS (6).

© 2010 March of Dimes Foundation. All rights reserved. The March of Dimes is a not-for-profit organization recognized as tax-exempt under Internal Revenue Code section 501(c)(3). Our mission is to improve the health of babies by preventing birth defects, premature birth, and infant mortality.