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Down syndrome risk estimation after normal genetic sonography
Anthony M Vintzileos1, Edwin R Guzman, John C Smulian
1Division of Maternal-Fetal Medicine, Department of Obstetrics, Gynecology and Reproductive Sciences, University of Medicine and Dentistry of New Jersey--Robert Wood Johnson Medical School/St Peter's University Hospital, New Brunswick, NJ, USA.
American Journal of Obstetrics and Gynecology
|November 20, 2002
Summary
A normal genetic sonogram significantly reduces the risk of fetal Down syndrome by 83% to 89%, regardless of the initial indication for testing. This finding aids in counseling high-risk pregnancies.
Area of Science:
- Prenatal diagnostics
- Maternal-fetal medicine
- Genetics
Background:
- Down syndrome is a leading indication for prenatal genetic testing.
- Genetic sonography is a non-invasive screening tool for fetal aneuploidies.
- Risk assessment for Down syndrome often involves maternal age and biochemical markers.
Purpose of the Study:
- To evaluate if risk reduction for fetal Down syndrome varies based on the indication for a normal genetic sonogram.
- To quantify the effectiveness of a normal genetic sonogram in reducing Down syndrome risk across different risk groups.
- To provide data for counseling pregnant women undergoing prenatal screening.
Main Methods:
- Second-trimester genetic sonograms were offered to pregnant women at increased risk for Down syndrome (>/=1:274).
- Indications included advanced maternal age (>/=35 years), abnormal triple screen, or both.
- Outcomes were determined by genetic amniocentesis, pediatric assessment, and birth follow-up. Normal sonography excluded ultrasound aneuploidy markers.
Main Results:
- The prevalence of Down syndrome decreased from 1.41% to 0.21% with a normal genetic sonogram.
- A normal genetic sonogram provided a 6.64-fold risk reduction for Down syndrome.
- Risk reduction ranged from 83% (advanced maternal age) to 89% (abnormal triple screen in younger women).
Conclusions:
- Normal genetic sonography consistently reduces Down syndrome risk across all indications.
- The risk reduction is substantial, ranging from 83% to 89% regardless of the initial risk factor.
- These findings support the use of genetic sonography in counseling high-risk pregnancies prior to amniocentesis.