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Moderate exercise is healthy for pregnant women and
their babies, but exercising too much
or too little could raise the risk of bearing a low birth weight baby.
The investigators found that women who exercised
strenuously five or more times a week during the last trimester
of their pregnancy had four times the
risk of having a low weight baby.
Women who exercised fewer
than three times a week were twice as
likely to have a low birth weight baby.
Low birth weight babies are believed to be more likely
to have subsequent health problems.
Pregnant women who exercised
three or four times a week seemed to have the best chance of having a
healthy weight baby.
Pregnancy is not the time to exercise excessively,
but it is also not the time to be sedentary. Moderate
exercise three to four times a week is perfectly
safe -- and may even be beneficial.
The investigators found that doing strenuous
exercise, such as aerobics classes, more than four times a
week increased substantially
the risk of having a low birth weight baby.
Other researchers have theorized that too much exercise
could possibly draw blood towards the mother's exercising muscles and
away from the developing fetus, depriving it of oxygen and nutrients.
The researchers found no evidence that a woman's level
of pre-pregnancy fitness had any affect on the association between exercise
and birth weight.
The researchers had expected that women who were fit
before pregnancy might be able to tolerate a high level of exercise without
affecting their baby's weight, but this was not the case. And women who
had not exercised did not increase their risk by starting to exercise
modestly while pregnant.
Staying sedentary did
increase their risk of delivering a low birth weight baby.
American Journal of Obstetrics
and Gynecology February 2001;184:403-408
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