Ultrasound screening of fetuses at increased risk for Down syndrome: how many missed diagnoses?

Prenat Diagn. 2006 Jan;26(1):22-7. doi: 10.1002/pd.1319.


Objective: To determine the number of Down syndrome (DS) fetuses identified, amniocenteses performed, and procedure-related losses incurred when second-trimester ultrasound is used to screen high-risk patients in order to determine who should undergo an amniocentesis.

Methods: A decision analytic model was designed for women at increased risk for a DS fetus due to either advanced maternal age (AMA) or a positive expanded maternal serum alpha fetoprotein (MSAFP) screening test, also known as a triple screen (+triple) test. The model compared: (1) the current standard of offering all at-risk women amniocentesis to (2) a policy of performing amniocentesis only when sonographic markers of DS are seen on ultrasound. Baseline assumptions included a sensitivity of 60.6% for targeted ultrasound and a screen-positive rate of 16.2%.

Results: If targeted ultrasound is used to determine whether high-risk patients should undergo amniocentesis, 56% (3933/7025) of all DS fetuses are missed. The diagnosis of DS is missed most frequently among women at highest risk for DS (AMA and +triple). In this subgroup of patients, there are 3152 DS fetuses in the second trimester, of which 2815 (89%) are identified by triple screen test. When an ultrasound screen is added, only 1709 (54%) of DS fetuses will be identified.

Conclusion: Substantially fewer DS fetuses will be detected when targeted ultrasound is used as a screen among already identified high-risk patients.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Decision Support Techniques*
  • Decision Trees
  • Down Syndrome / diagnostic imaging*
  • Female
  • Genetic Counseling
  • Humans
  • Predictive Value of Tests
  • Pregnancy
  • Pregnancy Trimester, Second
  • Sensitivity and Specificity
  • Ultrasonography, Prenatal*