IQ Scores: Different for Twins?
If So, Early Birth or Low Birth Weight Could Be Why, Study Shows
WebMD News Archive
Nov. 17, 2005 -- In a study from the U.K., twins scored slightly lower on IQ
tests than their single-birth siblings.
The small gap faded when early births and low birth weight were taken into
account. As expected, the twins were often born earlier and smaller than
But the researchers aren't totally satisfied with the findings. They didn't
get all the information they wanted, and the study's scope was limited. They
call for more work on the topic.
The researchers included Georgina Ronalds, MSc, of the London School of
Hygiene and Tropical Medicine. The study appears in BMJ Online
About the Study
Data came from a citywide study done in Aberdeen, Scotland, in the 1950s.
Children in Aberdeen took IQ tests administered at school when they were 7 and
9 years old.
At age 7, single-birth children scored about five points higher than their
siblings who were twins. At age 9, the gap had reached six points.
Twins' early births and lower birth weights may have been important, write
But there's more to the story than that.
Pros and Cons
All comparisons were done within families. So twins from Family A weren't
compared to single-birth kids from Family B.
That was done for consistency's sake. Lots of factors -- like family income
and parental education -- were taken into account.
However, about a fifth of the children that the researchers wanted to study
were left out. There was missing background information such as gestational age
at delivery, which would demonstrate premature birth.
More current data, with tests given by IQ experts, would have been a plus,
write Ronalds and colleagues.
It may not add up to a final verdict, but a possible hint about the benefits
of a long, healthy pregnancy for any baby, twin or not.