WEDNESDAY, Dec. 12 (HealthDay News) -- Children whose mothers
went into pregnancy overweight may have slightly lower scores on
certain tests of verbal and numbers skills, a new study says.
The findings, reported online Dec. 10 in the journal
Pediatrics, do not prove that their mothers' extra pounds
are the reason for these decreased scores, and experts not involved
in the study said it's too soon to suggest mothers-to-be lose
weight for the sake of their kids' mental prowess.
But the results do add to studies showing that, for whatever
reason, kids born to heavy mothers tend to have a somewhat lower IQ
than their peers.
For the study, researchers led by Emre Basatemur, of the
Institute of Child Health at University College London, combed data
on nearly 20,000 U.K. children involved in an ongoing national
study. The children took standard tests of verbal ability, numbers
skills and reasoning at the age of 5, and again at age 7.
In general, children scored slightly lower if their mother was
overweight going into pregnancy. The difference was very small,
though: For every 10-point increase in mothers' body-mass indexes
(BMI) -- an extra 60 pounds for an average-height woman -- kids'
test scores dipped slightly. BMI is a measurement of body fat based
on height and weight.
That dip in test scores was roughly equal to a 1.5-point decline
Exactly what difference that could make in real life is unclear,
said researchers not involved in the work. What's more, there is no
way to know whether mothers' extra weight is to blame.
Basatemur acknowledged that many factors, both genetic and
environmental, influence children's cognitive development. "The
association observed in our study accounts for a small amount of
the overall variation seen in children's cognition," he said.
Other experts emphasized that the study found only an
association. "Observational studies like this can never prove
cause-and-effect," said Dr. Ryan Van Lieshout, assistant professor
of psychiatry and behavioral neurosciences at McMaster University
in Hamilton, Ontario.
The researchers did try to account for other factors, such as
family income and parents' education. But they lacked some key
information -- including parents' IQ scores, said Van Lieshout, who
has studied the relationship between mothers' weight and kids'
"You can't conclude from this that women should try to attain a healthy weight before pregnancy in order to improve their child's cognition," Van Lieshout said.
A child behavior specialist agreed. One question is what
mothers' nutrition was like during pregnancy, said Andrea Vazzana,
clinical assistant professor of child and adolescent psychiatry at
NYU Langone Medical Center in New York City.
Since nutrition during pregnancy affects fetal development, it's
possible that differences in diet -- rather than weight, per se --
have some role in the findings.
But there were also problems in how the study assessed kids'
abilities, Vazzana said. Their verbal, reasoning and numbers skills
were each gauged with one test, or "scale." And that's not enough
to broadly capture children's abilities, she said.
There also was a lot of missing data, she pointed out. For
instance, the researchers had full information for only about half
of the children at age 7.
Still, Van Lieshout said that nine studies so far have looked at
the relationship between mothers' weight and children's mental and
behavioral development, and most suggest a link.
The question, though, is why. Van Lieshout said the "most
tantalizing" theory is that there could be something about mothers'
excess fat that affects fetal brain development. Animal research
has suggested that's possible, but no one knows if that's true in
For now, the experts said, there are plenty of reasons for women
to go into pregnancy as healthy as possible -- which includes being
neither substantially overweight nor underweight.
Basatemur said his study results should be interpreted alongside
existing weight recommendations. "The association observed in our
study may be a further reason to follow this advice, and reinforce
the need ... to reduce the prevalence of overweight and obesity in
women of childbearing age," he said.
Obesity can make it more difficult to get pregnant, and it
raises the odds of certain health problems for expectant mothers,
such as pregnancy-related diabetes and high blood pressure. Obesity
also has been linked to higher-than-normal risks of miscarriage,
stillbirth and birth defects.
Van Lieshout agreed that "there are absolutely reasons" to
strive for a healthy weight before pregnancy. "We just don't know
if this is one of them," he said.
Learn more about having a healthy pregnancy from the
U.S. Centers for Disease Control and
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