According to a new study accepted for publication in The Endocrine Society's Journal of Clinical Endocrinology & Metabolism (JCEM), regular moderate-intensity aerobic exercise led to a modest reduction
in offspring birth weight without restricting the development of
maternal insulin resistance.

There is a large body of
evidence demonstrating the influence of the in utero environment on
growth trajectory in postnatal life. Increased size at birth is
associated with greater risk for the development of obesity in
childhood. This study is the first to demonstrate a significant effect
of non-weight bearing exercise (such as stationary cycling) on birth

"Our findings show that regular aerobic exercise
alters the maternal environment in some way that has an impact on
nutrient stimulation of fetal growth, resulting in a reduction in
offspring birth weight," said Paul Hofman, MD, of the University of
Auckland in New Zealand and co-author of the study. "Given that large
birth size is associated with an increased risk of obesity, a modest
reduction in birth weight may have long-term health benefits for
offspring by lowering this risk in later life."

This study is
also the first to evaluate changes in insulin sensitivity in response
to aerobic exercise training during pregnancy. Maternal insulin
resistance is essential in increasing nutrient availability to the
fetus and has been correlated with birth size. Exercise has been shown
to reduce insulin resistance but a major reduction in insulin
resistance may adversely affect a pregnancy by severely restricting
fetal nutrition. However, findings from this study suggest that regular
exercise during pregnancy does not cause the same reduction in insulin
resistance that occurs in exercising non-pregnant individuals.

physiological response to pregnancy appears to supersede the chronic
improvements in insulin sensitivity previously described in response to
exercise training in non-pregnant individuals," said Hofman. "This may
be an important finding for athletes who want to continue regular
training during their pregnancy as it suggests that training will not
have a major adverse impact on insulin resistance."

In this
randomized trial, researchers assigned 84 first-time mothers to either
exercise or control groups. Participants in the exercise group utilized
stationary cycling and were individually prescribed to a maximum of
five sessions of 40 minutes of aerobic exercise per week. The exercise
group was instructed to maintain the exercise program until at least 36
weeks gestation. Insulin sensitivity was assessed at 19 and 34-36 weeks
gestation using an intravenous glucose tolerance test. Birth weight and
BMI at birth were measured within 48 hours of birth.

training had no effect on maternal body weight or BMI during late
pregnancy. Furthermore, exercise had no effect on insulin resistance
from baseline to late gestation, and did not affect any other
parameters of glucose regulation. Offspring of exercisers were on
average 143 â± 94 grams lighter than their control counterparts, however
there was no difference in birth length. Exercise training also
resulted in lower offspring BMI.

researchers working on the study include: Sarah Hopkins, Wayne Cutfield
and Lesley McCowan of The University of Auckland in New Zealand; and
James Baldi of Northern Arizona University in Flagstaff, Ariz. The
article, "Exercise Training in Pregnancy Reduces Offspring Size without
Changes in Maternal Insulin Sensitivity," will appear in the May 2010
issue of JCEM.

Founded in 1916, The Endocrine
Society is the world's oldest, largest and most active organization
devoted to research on hormones and the clinical practice of
endocrinology. Today, The Endocrine Society's membership consists of
over 14,000 scientists, physicians, educators, nurses and students in
more than 100 countries. Society members represent all basic, applied,
and clinical interests in endocrinology. The Endocrine Society is based
in Chevy Chase, Maryland. To learn more about the Society and the field
of endocrinology,


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