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Nov. 30, 2009 -- The prevalence of infants born with Down syndrome has increased dramatically in recent years, new research indicates.
Reporting in the Nov. 30 issue of Pediatrics, scientists say the prevalence of live born infants with Down syndrome increased by 31% between 1979 and 2003, from 9 to 11.8 per 10,000 live births in the 10 U.S. regions studied.
That represents an average increase of 0.9% per year, the study shows.
The researchers analyzed data from 10 population-based birth registries in the U.S., estimating prevalence at birth among children up to age 19 in each region, and also in all of the areas together.
During the periods studied, "prevalence at birth significantly increased among births to older mothers and decreased slightly among births to younger mothers."
Maternal age (age 35 and older) is a known risk factor for having a child with Down syndrome, the most common chromosomal disorder.
"The overall [Down syndrome] prevalence at birth was almost five times higher among births to older mothers (38.6 per 10,000) than among births to younger mothers (7.8 per 10,000)," the researchers write.
The study also shows that:
"Our study also confirmed an increase in prevalence in [Down syndrome] at birth over time, and this trend over time paralleled the increasing proportion of births to older mothers," the researchers write.
The researchers say their findings could reflect an increasing proportion of births to older mothers, and improvements in the survival of infants with the genetic disorder. People with Down syndrome are at increased risk for medical problems such as heart defects, hearing and vision problems, and respiratory problems.
The number of children, adolescents, and adults with Down syndrome is likely to increase and people with the condition are likely to live longer, the researchers note.
The authors say in a news release that their findings may be useful in determining the number of people with Down syndrome and in the development of policies to help them.