Ultrasound markers that can be detected in the second trimester of pregnancy are strongly predictive for Down's syndrome, show findings from a systematic review and meta-analysis.
The team found that nine markers significantly increased a child's risk for having Down's syndrome to differing degrees if present.
"The detection of any one of the findings during the scan should prompt the sonographer to look for all other markers or abnormalities," said study author Kypros Nicolaides (Harris Birthright Research Centre for Fetal Medicine, London, UK) in a press statement.
Overall, 48 studies were included in the analysis. To be included they had to have analyzed second trimester sonographic findings and describe both trisomy 21 and euploid fetuses.
The team found that the most strongly predictive feature was dilated brain ventricles, which increased the likelihood for Down's syndrome 25-fold, followed by having a small or absent nose bone, an abnormal artery to the upper extremities, and a thicker than normal back of the neck, which each increased the likelihood 23-, 21-, and 19-fold, respectively. The other findings were associated with smaller but still significant risk increases if present, ranging from fourfold to 11-fold.
Absence of individual features reduced the risk for Down's syndrome by 6-54%, and combined absence of all nine sonographic markers reduced the risk more than sevenfold.
"Further studies are needed to establish reference ranges for each biometric marker and to estimate the effect of gestational age on screening performance," write the authors in Ultrasound in Obstetrics and Gynecology, although they concede that widespread first trimester screening and termination of many fetuses with trisomy 21 may make this impossible.
"In the interim the data arising from this meta-analysis and their interpretation could form the basis for clinical practice," they say, although they emphasize the importance of appropriate ultrasound training for those carrying out such scans.
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