June 5, 2003
Women
pregnant with boys tend to eat about 10 percent more calories
a day than those carrying girls but don’t gain more
weight, new research indicates. The study, published this
week in the British Medical Journal, appears to explain — at
least in part — why newborn boys are heavier than
girls and suggests that signals between the fetus and the
mother
drive the appetite during pregnancy.
Boys are on the average 3.5 ounces heavier at birth
than girls. The study by researchers from the Harvard School
of
Public
Health and the Karolinska Institute in Stockholm, Sweden, is
the first
to examine whether that difference could be due to the mother
eating more.
The scientists assessed the diets of 244 American women one
week before they came to the hospital for a routine prenatal
checkup
at 27 weeks of pregnancy. All the women later gave birth to
normal-weight babies at full term.
APPETITE ‘DRIVEN BY THE FETUS’
The researchers found that women who gave birth to boys were
consuming about 10 percent, or 200, more calories per day than
those who went on to have girls. Yet the amount of weight mothers
gained during pregnancy did not differ between those who had
girls and those who had boys.
“This sounds undoubtedly driven by the fetus,” said Kent
Thornburg, a fetal physiologist at Oregon Health Sciences University
who was not connected with the study.
Thornburg said the findings do not necessarily mean that boys
are heavier solely because their mothers eat more.
“That would lead to the conclusion that the more
a pregnant woman eats the bigger her baby will be and that
female babies would
be larger if only their mothers ate more,” he said. “A
more realistic hypothesis is that fetuses stimulate the appetite
in their mothers in proportion to their requirement for optimal
growth.”
Scientists do not understand exactly what causes appetite to
increase during pregnancy, but the study’s findings suggest
there is a chemical communication between mother and fetus
so that males can grow faster than females, with the mother
being
signaled to eat more to enable that growth, Thornburg said.
Thornburg said the findings could be relevant to the recently
discovered
relationship between growth in the womb and the risk in adulthood
of illnesses such as heart disease and diabetes.
“A decade ago, we thought that the primary risk for
chronic disease in any apparently healthy baby was solely the
result of genetic
endowment from parents,” Thornburg said. “We now
know that the access to nutrients by the fetus is important
in determining prenatal growth rate and thus lifelong health.”
The study’s authors said their results
indicate that male fetuses may be more vulnerable than female
ones to problems linked to fetal nutrition.
© 2003 Associated Press
