A new analysis has found that some second trimester markers for Down’s syndrome that are detected by ultrasound are more important than other markers for the disease. Insights from this research should help adjust pregnant women’s risks for having a child with the disorder.
Down’s syndrome screening is offered to all pregnant women, starting with a background risk based on their age. Specific characteristics identified during a second trimester ultrasound scanning are possible markers for Down’s syndrome, and they include increased thickness of the back of the neck, dilated brain ventricles, absent or small nose bone, 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, Kypros Nicolaides, MD, from the Harris Birthright Research Center for Fetal Medicine at King’s College London (UK), and his colleagues analyzed all published data that reported findings on second trimester markers for Down’s syndrome between 1995 and 2012. The findings were published early online January 24, 2013, in the journal Ultrasound in Obstetrics & Gynecology.
The researchers identified 48 studies, and they discovered that most single markers have only a small effect on modifying the risks for Down’s syndrome. This finding could have important clinical implications because currently in the United States, when a marker such as a thighbone or short arm is identified, women are told that they are at high risk of having a child with Down’s syndrome. However, Dr. Nicolaides and his coworkers discovered that a few markers do carry increased risks. Increased thickness of the back of the neck, dilated brain ventricles, 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.
“The detection of any one of the findings during the scan should prompt the sonographer to look for all other markers or abnormalities,” said Prof. Nicolaides. He added that the study also revealed that if a detailed second trimester ultrasound scan shows the absence of all major markers, the risk of having an infant affected by Down’s syndrome is decreased by more than seven-fold.
The study findings implied that the comparative significance of ultrasound markers is very different from what has been earlier believed. Prof. Nicolaides noted that these findings will be incorporated in obstetric ultrasound scan software that adjusts women’s risks for having a child with Down’s syndrome.
Harris Birthright Research Centre for Fetal Medicine at King’s College London