Using second trimester ultrasound to detect Down's syndrome fetuses results in more fetal losses due to amniocentesis than cases of Down's detected, according to a new meta analysis.
The analysis, which looked at 56 studies involving 1930 fetuses with Down's syndrome and 130,365 unaffected fetuses, found that examining the nuchal fold at the back of the fetus' neck was a poor way to detect affected babies. Using this method resulted in a high rate of false positive diagnoses. Further more, say the researchers, between 4454 and 87,413 women at average risk of an affected fetus would need to be scanned to detect one case of Down's.
The researchers also note that using ultrasound to select women for amniocentesis increases the number of healthy babies lost as a complication of the procedure. Also recognised is the enormous stress caused by a false positive ultrasound. Even when a subsequent scan shows the baby to be healthy, many mothers continue to believe that there must be something wrong with their babies (J Am Med Assoc, 2001; 285: 1044-55).