The percentage of children born with Down syndrome has increased by about one percent per year since 1979, according to new findings from the Centers for Disease Control and Prevention (CDC).

The increase is probably because more and more women 35 and over are having babies, Dr. Adolfo Correa of the CDC’s Center for Disease Control’s National Center on Birth Defects, one of the study’s authors, said. These older women are five times more likely than younger moms to have a baby with Down syndrome, Correa pointed out.

Today, about one in 1,000 children and adolescents in the US has the chromosomal disorder, and about 5,400 children are born with Down syndrome in the US every year, Correa and his colleagues note in the journal Pediatrics.

People with Down syndrome have some degree of mental retardation, and are also at risk of certain health problems; for example many are born with heart defects. But 90 percent will celebrate their fifth birthdays, and the average life expectancy for a person with Down syndrome is over 50.

To date, the researchers note, just one study done in a single city has looked at Down syndrome rates in children and adolescents. Accurate figures are necessary, they add, to plan for health care services for these individuals as they get older, because many may need specialized care.

Correa and his team analyzed birth defect registry data from 1979 to 2003 for 10 different US regions to come up with these numbers.

On average, they found, 9 in every 10,000 babies born live in the US in 1979 had Down syndrome. That figured increased by more than 30 percent over the next 14 years, reaching nearly 12 per 10,000 babies in 2003.

In 2002, the researchers estimate, there were about 83,400 people 19 and under with Down syndrome.

The risk of Down syndrome was higher among boys than girls, Correa and his colleagues found. There was also evidence that Down syndrome was more common among Hispanics and whites, but less common among African-Americans, but Correa said it’s not clear why.

The findings are “a good starting point” to better predict the medical needs of people with Down syndrome, the researcher said. What the findings couldn’t show, he added, is whether or not the increase in women undergoing prenatal screening has meant fewer babies are being born with Down syndrome.

SOURCE: Pediatrics, December 2009.