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Can sonographers reliably identify anatomic features associated with Down syndrome in fetuses?
B R Benacerraf1, A Cnann, R Gelman
1Department of Obstetrics and Gynecology, Brigham and Women's Hospital, Boston, MA.
Radiology
|November 1, 1989
Summary
Standardizing femur length measurements can help identify fetuses at risk for Down syndrome. Combining femur length with nuchal fold measurements improves detection rates in ultrasound screenings.
Area of Science:
- Medical Imaging
- Prenatal Diagnostics
- Fetal Ultrasound
Background:
- Down syndrome screening relies on various fetal biometrics.
- Femur length is a key indicator, but standardization is needed for accuracy.
- Sonographer variability can impact measurement reliability.
Purpose of the Study:
- To establish a standardized method for femur length measurement in Down syndrome risk assessment.
- To evaluate the effectiveness of femur length and nuchal fold measurements in identifying Down syndrome fetuses.
- To assess the feasibility of these measurements in routine sonographic practice.
Main Methods:
- Regression analysis was used to correlate biparietal diameter with femur length in 709 normal fetuses.
- A formula was derived: expected femur length = -9.3105 + 0.9028 * biparietal diameter.
- Measurements were performed by eight sonographers on 20 Down syndrome and 709 control fetuses.
Main Results:
- A measured-to-expected femur length ratio of ≤0.91 identified Down syndrome with 40% sensitivity and 95% specificity.
- The positive predictive value for this ratio was 3.1%.
- Incorporating a thickened nuchal fold (≥6 mm) increased sensitivity to 45% and positive predictive value to 4.3%.
Conclusions:
- Standardized femur length measurement, combined with nuchal fold assessment, can aid in Down syndrome risk identification.
- The proposed method is achievable in typical ultrasound laboratories with sonographer-performed measurements.
- This approach offers a practical tool for enhancing prenatal screening for Down syndrome.