Twins' IQ no longer sub-par, study shows

By Megan Rauscher

NEW YORK (Reuters Health) - The academic performance of twins is just as good as that of single-born children, according to a new study published online in the British Medical Journal. The finding runs counter to earlier research that found twins had lower IQs than singletons.

Today, "one in 25 newborns is a twin, the highest ever due to infertility treatment," Dr. Kaare Christensen from the University of Southern Denmark in Odense pointed out in comments to Reuters Health. "Twins are born early and small, which makes parents worry about their future."

Science has contributed to the anxiety by showing that twins born before World War II had a 4- to 5-point lower IQ score on average. A Scottish paper published just last year entitled "The Cognitive Cost of Being a Twin" argued that twins are mentally disadvantaged; however, the twins in the study were born in the 1950s.

In a more modern group of twins, Christensen's team found that twins have similar school performance as single-born children, despite weighing on average 908 grams less than single-born infants at birth. The findings are based on a review of ninth grade test scores for 3,411 twins and a random sample of 7,796 singletons born during 1986 to 1988.

Actually, twins performed slightly better than singletons on math tests, they noticed.

"For parents, school performance is more important than IQ," Christensen said, "so twin families should not be more worried (about academic performance) than other families."

The researchers think that improvements in obstetric and pediatric care over the past 50 years have "largely ameliorated the cognitive disadvantage identified in twins by earlier research."

SOURCE: British Medical Journal, online September 29, 2006.