Screening for Down’s syndrome is offered to all pregnant women who start out with a background risk based on their age. Certain features detected during a second-trimester ultrasound exam are potential markers for Down’s syndrome, and they include dilated brain ventricles, absent or small nose bone, increased thickness of the back of the neck, an abnormal artery to the upper extremities, bright spots in the heart, ‘bright’ bowels, mild kidney swelling, and shortening of an arm bone or thigh bone.
To determine how these markers affect risk, researchers at the Harris Birthright Research Centre for Fetal Medicine, King’s College London, analysed all published studies that reported results on second-trimester markers for Down’s syndrome between 1995 and 2012.
The researchers identified 48 studies and discovered that most single markers have only a small effect on modifying the odds for Down’s syndrome. However, the study found that a few markers do carry increased risks. Dilated brain ventricles, increased thickness of the back of the neck, and an abnormal artery to the upper extremities increase the risk by three-to four-fold, and an absent or small nose bone increases the risk by six-to seven-fold.
Kypros Nicolaides, Professor of Fetal Medicine at King’s, said: ‘The detection of any one of the findings during the scan should prompt the sonographer to look for all other markers or abnormalities.’ He added that, if a detailed second-trimester ultrasound exam demonstrates the absence of all major markers, the risk of having a baby affected by Down’s syndrome is reduced by more than seven-fold.
The findings indicate that the relative importance of ultrasound markers is very different from what has been previously assumed. Professor Nicolaides noted that the results from this study will be incorporated in obstetric ultrasound scan software that adjusts women’s risks for having a child with Down’s syndrome.
Notes to editors
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