Exercise During Pregnancy for Smaller Baby
Moderate Exercise During Pregnancy Lowers Baby's Birth Weight, May Reduce Baby's Risk of Obesity
April 5, 2010 -- Women who exercise moderately during pregnancy give birth
to somewhat smaller babies, which may reduce the infants' obesity risk later,
according to a new study.
The average birth weight of babies born to exercising mothers was lower but
still very healthy.
The average birth weight of babies born to mothers who exercised was 7.5
pounds, compared to 7.8 pounds for mothers who did not exercise, says a team of
researchers from New Zealand and the U.S. Babies born weighing 8.8 pounds
or more are defined as high birth weight.
At the two-week checkup, the babies of exercising moms averaged 8.1
pounds; the babies of sedentary moms averaged 8.6 pounds.
"We would suggest this study support the recommendations of at least 30
minutes of moderate exercise daily and probably more," says study co-author
Paul Hofman, MD, a researcher at the University of Auckland in New Zealand. The
study is published in the Journal of Clinical Endocrinology &
The new research follows a
recent study finding that three out of four pregnant women in the U.S. do
not get enough exercise.
Exercise During Pregnancy: The Study
Hofman and his colleagues assigned 84 women pregnant with their first child
to an exercise group or a control group. Women in the exercise group rode
stationary bikes at home at a moderate intensity for 40 minutes, 5 times a week
maximum, beginning at 20 weeks into the pregnancy and continuing until about
Women in the control group were instructed to continue their normal daily
activities during the same time periods.
Women in both groups had, on average, a healthy body weight before pregnancy
and were similar in other regards such as age and ethnicity.
Exercise During Pregnancy: Results
The babies born to the exercisers had a lower body weight and a lower body
mass index or BMI.
There were no differences in the length of the babies, on average, between
exercisers and non-exercisers. The exercise didn't affect the length of the
pregnancy, either, or the mothers’ weight.
Exactly why the exercising mothers produced smaller babies isn't
known, says study co-author Chris Baldi, PhD, an assistant professor of
biological sciences at Northern Arizona University, Flagstaff.
Researchers initially believed the exercising mothers would become less
insulin-resistant. Typically, Baldi says, a woman becomes more
insulin-resistant during pregnancy, a normal occurrence within certain
boundaries. "It has a lot to do with hormonal changes," he says. If a woman
becomes too insulin-resistant, gestational diabetes can occur.
"It did not come out as we suspected," Baldi tells WebMD, with no
substantial differences found in insulin resistance between the two groups.
The difference, says Baldi and Hofman, may be because of other factors, such
as differences found in certain growth factors. Another possible explanation,
Hofman says, is slightly reduced blood flow that occurs to the placenta during
exercise and for several hours afterward.