MONDAY, Oct. 29, 2001 (HealthDayNews) -- When it comes to developing dyslexia and related reading disorders, Jack may face different risk factors from Jill, new research says.
A study of almost 5,000 Minnesota children shows that variations in birth weight between girls significantly affects their reading ability later in life. But the weight factor doesn't seem to matter much for boys -- they're at increased risk of learning disabilities to begin with.
Low birth weight has become more common as the rate of premature delivery has climbed. The incidence of preemie births has jumped sharply in the last decade, in large part because of increased use of fertility treatments that promote multiple pregnancies. Preemie births -- before 37 weeks of gestation -- account for about 11 percent of all deliveries in the United States.
Roughly 1 percent of preemies are considered extremely low birth weight, or under 1,500 grams (about 3.3 pounds). Many of these children show signs of significant cognitive trouble by age 8, including poor academic performance and learning disabilities.
"We don't know why, but boys do have a higher mortality in the newborn period and seem to have more difficulties in learning development" as they get older, says Dr. Saroj Saigal, a pediatrician at McMaster University in Hamilton, Ontario, who studies the effects of birth weight on childhood development.
Typically, boys have more trouble with reading, while girls struggle with mathematics, Saigal says.
In the latest study, which appears in the Nov. 1 issue of the American Journal of Epidemiology, researchers at the Mayo Clinic studied 303 children with dyslexia and other reading problems and compared them to about 4,500 other kids without such difficulties. The work is part of a larger look at childhood development in Olmsted County -- which includes the Mayo's hometown of Rochester, Minn. -- involving students born there between 1976 and 1982.
As expected, boys were 2.5 times as likely as girls to develop dyslexia, the researchers say. But girls born light for their age at birth -- weighing less than 2,500 grams, or about 5.5 pounds -- were 3.5 times more likely than normal-weight girls to have reading disorders.
On the other hand, both lightweight and normal-weight boys were more than twice as likely as normal-weight girls to run into trouble reading. However, the odds that a boy would develop dyslexia didn't hinge on his weight at birth. The researchers speculate that the weight factor in boys is dwarfed by their heightened risk of reading woes overall.
The researchers also found that girls whose mothers didn't finish high school were about twice as prone as girls with better-educated mothers to learning difficulties. And girls seemed shielded from dyslexia when their fathers were at least 35 years old at their birth.
For boys, the only parental factor that appeared to hamper reading was if their fathers -- but not their mothers -- had finished high school. If not, their risk of dyslexia doubled.
Jennifer St. Sauver, a Mayo epidemiologist and lead author of the study, says the parental education influence on a child's dyslexia risk may involve socialization at home. For example, better-educated mothers may concentrate more than dropouts on their daughters' schooling, while the same trend may apply between fathers and sons.
However, she adds, the finding that girls born to older fathers read better "was really puzzling."
"We don't have a good explanation for that. Maybe older fathers are more interested in their daughters' education, but again that's just conjecture," she says.
St. Sauver's group is now analyzing preliminary data on gender differences and math skills.
What To Do
For more on the care preemies receive, check out Neonatology or the Baby Zone.
To learn more about dyslexia, try the International Dyslexia Association or the Dyslexia Parents Resource.
To learn more about developmental problems, visit the Developmental Disabilities Health Alliance.
