Ultrasound detection of Down syndrome: is it really possible?

Several ultrasonographic signs have been described in second-trimester fetuses at high risk for Down syndrome. We examined these parameters in twin pregnancies in which one fetus was affected with Down syndrome and the other was normal. Biparietal diameter to femur length ratio was concordant (either normal or abnormal) in eight of nine sets of twins. Actual femur length to expected femur length ratio was concordant in seven of nine sets of twins. Nuchal fold thickening (6 mm or more) correctly identified five out of nine affected fetuses and was not present in any of the normal fetuses. In conclusion, neither ratio was helpful in differentiating the fetus with Down syndrome from its normal cotwin. A thickened nuchal fold was the most informative parameter examined.