Almost 80% of Down syndrome cases can be detected with a new non-invasive formula using a ratio of skin thickness and limb measurements, Yale researchers report in a study published in the May issue of American Journal of Obstetrics and Gynecology.
This detection method cuts down on the need for amniocentesis, an invasive method of detecting Down syndrome that has a risk of miscarriage. The new formula was devised by the study's first author, Ray O. Bahado-Singh, M.D., associate professor of obstetrics and gynecology at Yale School of Medicine and Utku Oz, research fellow.
Down syndrome is a congenital disorder caused by the presence of an extra 21st chromosome. Those affected have mild to moderate retardation, short stature and a flattened facial profile. Women over age 35 are at a higher risk of giving birth to a child with Down syndrome.
Bahado-Singh's co-author, Joshua A. Copel, M.D., said that an increasing number of women are going to their doctors for non-invasive Down syndrome evaluation. "Over the last ten to fifteen years, there's been a shift in the mindset of women who come to us for prenatal diagnosis," said Copel, professor of obstetrics and gynecology at Yale. "Far more women are requesting that ultrasound be used along with the standard tools such as maternal age and maternal blood tests to improve Down syndrome risk-prediction. For years, we've been working on non-invasive ways of determining the risk factors so women can make more informed decisions based on the outcomes."
Copel said that two of the common physical findings of Down syndrome are that the upper arm bone (humerus) tends to be shorter than average and the skin at the back of the neck (nuchal) tends to be thicker. The individual differences are subtle, making detection difficult. Ultrasounds done at sixteen weeks show a difference of millimeters.
To try to improve the detection rate, Bahado-Singh, Copel and their research team took the ratio of the upper arm measurement and the neck measurement and multiplied it by the age-related risk to better predict Down syndrome. Using this method, which is called an ultrasonographic biometry algorithm, in their study, they compared 94 cases of Down syndrome and 4,700 normal fetuses. There was a 70.8% detection rate for Down syndrome with about 20% of patients being test-positive. This is an increase over maternal age combined with either one of the measurements.
"By taking the ratio of a measurement of the upper arm and a measurement of the neck, we were able to improve the detection rate over either of these methods alone," Copel said.
Copel said there is a possibility that the results are population-specific to southern Connecticut, so the study needs to be replicated by other researchers. The team's future work will focus on fairly simple measurements that can be done at the bedside to give people better Down syndrome risk estimates. "This will help us target the best candidates for amniocentesis," said Copel. "We can reduce the risk in the vast majority of women, while keeping a high detection rate."
In the near future, Bahado-Singh and the team would like to be able to do an ultrasound, take a few quick measurements and immediately be able to give a couple the risk estimates for Down syndrome. "This would mean fewer amniocenteses and a higher percentage of abnormal babies identified," said Copel. These less-invasive detection methods can also become cost-effective alternative to amniocenteses, which cost up to $1,000.
Other researchers on the study included Utku Oz, M.D., Chaur-Dong Hsu, M.D., Ozgur Deren, M.D., and Maurice Mahoney, M.D.
For further information, Copel can be reached at (203) 785-2671 and Bahado-Singh can be reached at (203) 785-3091 or 203-785-5682.
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