Women who briskly walk for 33 minutes or more per day during the first trimester of pregnancy are more likely to deliver small-for-gestational-age infants and are at a decreased risk of delivering large-for-gestational-age infants, according to a new study.
The study was published by the American Journal of Epidemiology and authored by a University of Tennessee reproductive and perinatal epidemiologist Samantha Ehrlich.
According to the university, Ehrlich is interested in whether maternal exercise can alter an individual’s blueprint and “program” a fetus for future health outcomes.
Researchers said they examined exercise during the first trimester by looking at data from over 2,000 women receiving prenatal care at Kaiser Permanente Northern California. According to the report, 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."
The study found that 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," the report said.
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.
“There is evidence in animal models that maternal exercise may affect offspring metabolism—often referred to as fetal programming,” Ehrlich, an assistant professor in the Department of Public Health, said. “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.”
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, according to the university.
“Data on exercise early in pregnancy would be useful to health care providers counseling women who are planning a pregnancy,” said Ehrlich.