Fetal Nasal Bone Predicts Down Syndrome
Ultrasound Finding May Reduce Need for Amniocentesis
"A woman who is 40 has a one in 80 chance of having a baby with Down [syndrome], but if the nose is normal the risk is one-third of that, or one in 240," Nicolaides says. "For a 35-year-old woman with a background risk of one in 300, that risk is lowered to one in 1,000. A woman who knows this would be much less likely to accept the risks of amnio."
Genetic ultrasound expert Anthony Vintzileos, MD, tells WebMD that studies he and several other researchers have conducted on nasal bone development in fetuses suggests that the sensitivity of the observation is lower than that found in the new study. Nasal bone was absent in 41% of the fetuses with Down syndrome that he studied, and other studies also suggest this rate of sensitivity.
"From the clinical utility point of view the presence of the nasal bone may not mean much, because we found that more than half of the Down fetuses had it," he says. "But if you don't find it there is clearly something wrong."
Rebecca Smith-Bindman, MD, who conducted the analysis of past ultrasound studies, says it is not yet clear whether ultrasound screening represents an advance over serum blood screening, which, she adds, is widely underutilized in the United States.
"We ignore the best current methods to estimate risk, and still rely far too heavily on maternal age to determine who should and should not have amniocentesis," she says. "Serum blood testing could reduce the need for amnio in older women by 75%."