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Women exercising.

Women who exercise at the recommended levels during the first trimester of pregnancy—that is, about 33 minutes of brisk walking or more every day—are at increased risk of delivering small-for-gestational-age infants and decreased risk of delivering large-for-gestational-age infants, according to a new study published in the American Journal of Epidemiology and authored by Samantha Ehrlich, a reproductive and perinatal epidemiologist at the University of Tennessee, Knoxville.

Ehrlich is interested in whether maternal exercise can alter an individual’s blueprint and “program” a fetus for future health outcomes. Infant size at birth predicts health outcomes later in life; being born small or large is associated with increased risks of cardiovascular disease, obesity, and type 2 diabetes.

“There is evidence in animal models that maternal exercise may affect offspring metabolism—often referred to as fetal programming,” said Ehrlich, an assistant professor in the Department of Public Health. “If this programming occurs in humans, exercise performed early in the pregnancy would likely be the mechanism, as this is when the fetal metabolic blueprint is being laid out.”

In the study, researchers examined exercise during the first trimester by looking at data from over 2,000 women receiving prenatal care at Kaiser Permanente Northern California. The women reported their exercise behavior since becoming pregnant via the Pregnancy Physical Activity Questionnaire—a population-specific, validated survey used internationally by maternal health researchers—at 10-13 weeks pregnancy. The infants’ birthweights were compared to national data to determine which were small or large for their gestational age at birth.

High levels of exercise during early gestation were associated with the birth of more small-for-gestational-age infants and fewer large-for-gestational-age infants in analyses of the full cohort. Similar findings were observed among the underweight and normal weight women, but no associations were found among those with overweight or obesity.

Pregnant women are advised to participate in at least 30 minutes of moderate intensity exercise most days of the week. However, little is known about the effects of exercise specifically in early gestation on birth outcomes because most previous research in this area has focused on exercise in later stages of pregnancy.

“Data on exercise early in pregnancy would be useful to health care providers counseling women who are planning a pregnancy,” said Ehrlich.

The research was supported by the National Institute of Diabetes and Digestive and Kidney Diseases under grants K01DK105106 and P30DK092924, and by the National Institute of Environmental Health Sciences grant R01ES019196. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.


Karen Dunlap (865-974-8674,

Jules Morris (865-719-7072,