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Results
By Mayo Clinic staff
Your health care provider will use your age and the results of the blood test and ultrasound exam to gauge your risk of carrying a baby who has Down syndrome or Edwards syndrome. Other factors, such as your personal or family health history, also may affect your risk. Your health care provider or a genetic counselor will help you understand this risk and what it means for your pregnancy.
First trimester screening results are given as positive or negative and also as a probability, such as a 1 in 5,000 risk of carrying a baby who has Down syndrome. Generally, the test is considered positive if the risk is 1 in 300 or higher.
First trimester screening correctly identifies about 85 percent of women who are carrying a baby who has Down syndrome. About 5 percent of women have a false-positive result, meaning that the test result is positive but the baby doesn't actually have Down syndrome.
When you consider your test results, remember that first trimester screening only indicates your overall risk of carrying a baby who has Down syndrome or Edwards syndrome. A low-risk result doesn't guarantee that your baby won't have one of these conditions. Likewise, a high-risk result doesn't guarantee that your baby will be born with one of these conditions.
Often, abnormal test results are an invitation to consider further diagnostic testing — such as chorionic villus sampling or amniocentesis. These tests are more invasive than is first trimester screening and carry a slight risk of miscarriage, but they give more specific information about your baby's health. Having one of these tests is the only way to determine before birth whether your baby is affected by Down syndrome or Edwards syndrome.
The bottom line: Discuss the test results with your health care provider. A genetic counselor also can help you understand your options.
- Canick JA, et al. First trimester and integrated screening for Down syndrome and trisomy 18. http://www.uptodate.com/home/index.html. Accessed March 8, 2010.
- Benacerraf BR. Sonographic findings associated with aneuploidy. http://www.uptodate.com/home/index.html. Accessed March 8, 2010.
- Chervenak FA, et al. Ethical considerations in first-trimester Down syndrome risk assessment. Current Opinion in Obstetrics and Gynecology. In press. Accessed March 8, 2010.
- Kagan KO, et al. Screening for trisomy 21 by maternal age, fetal nuchal translucency thickness, free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A. Ultrasound in Obstetrics & Gynecology. 2008;31:618.
- Screening for birth defects. American Congress of Obstetricians and Gynecologists. http://www.acog.org/publications/patient_education/bp165.cfm. Accessed March 8, 2010.
- Routine tests in pregnancy. American Congress of Obstetricians and Gynecologists. http://www.acog.org/publications/patient_education/bp133.cfm. Accessed March 8, 2010.
- Harms RW (expert opinion). Mayo Clinic, Rochester, Minn. April 11, 2010.
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