Federal guidelines issued in 2008 recommend levels of physical activity for pregnant women that are meant to help ensure their physical and mental health, but analyses of data from four rounds of the National Health and Nutrition Examination Survey (NHANES) suggest that only a minority of women meet these goals.1 According to the guidelines, healthy pregnant women who were not highly physically active before becoming pregnant should get at least 150 minutes of aerobic exercise of moderate intensity per week, and those who were already physically active or who regularly engaged in vigorous activity need not reduce their activity level; for more active women, the guidelines recommend 75 minutes a week of vigorous activity or an equivalent combination of moderate and vigorous activity. During the period 1999–2006, some 14% of pregnant NHANES respondents reported meeting the first of these recommendations, and 23% the second. Women who were in their first trimester, were white or had health insurance had elevated odds of reporting the recommended activity level. The study period predates the federal guidelines, but includes the first four years after the American College of Obstetricians and Gynecologists (ACOG) released similar recommendations (calling for at least 30 minutes of moderate exercise on most days).

NHANES is conducted every two years among a nationally representative sample of adults and children. The questionnaire contains items on respondents’ usual daily activities, including a broad range of household, leisure and transportation-related activities. Analysts pooled data from four rounds of the survey, spanning the years 1999–2006, to study physical activity among pregnant women who were at least 16 years old. They used chi-square and F tests to examine changes over time and multivariable logistic regression to identify predictors of physical activity. Because the ACOG guidelines came out in 2002, the analysis of time trends compared 1999–2002 results with findings for 2003–2006.

The pooled data set included 1,280 pregnant women, who were, on average, 27.5 years old and five months pregnant. Fifty-five percent of the women were white, 21% were Hispanic and the rest belonged to other racial or ethnic groups; the majority were married (64%) and had more than a high school education (57%). More than eight in 10 had health insurance, and about one in 10 smoked.

Responses to questions about daily activities in the previous month indicated that 14% of pregnant women met the weekly recommendation for moderate physical activity (defined in NHANES as activity that “causes light sweating or a slight to moderate increase in breathing or heart rate”). Twenty-three percent met the goal for moderate to vigorous activity (the latter is defined as activity that “causes heavy sweating or large increases in breathing or heart rate”). The most frequently reported leisure activities were walking (cited by 41% of women), recreational activities (19%) and indoor aerobic exercises (12%). In 2003–2006 (the only years in which the relevant questions were asked), nearly all women spent some time each day watching television, and 15% spent five hours or more; three-quarters spent an hour or less using a computer outside work hours. Half of women over the entire study period said that they were less active at the time of the interview than they had been a year earlier, and three in 10 said that they were less active than were others of their age.

Overall, the proportion of pregnant women who engaged in moderate to vigorous activity, as well as the amount of time women spent in such activity, was unchanged between 1999–2002 and 2003–2006. However, between the two periods, the proportion reporting moderate to vigorous household activity increased from 49% to 60%, and the proportion reporting moderate leisure activity grew from 47% to 58%.

Three characteristics were -associated with measures of physical activity in the mul-tivariate analyses. Women in their first trimester, whites and women who had health insurance spent more time engaged in moderate to vigorous leisure activity than did women in their third trimester, nonwhite non-Hispanics and uninsured women, respectively (betas, 0.8–1.4). Each of these groups also had an elevated likelihood of meeting the recommendation for moderate to vigorous physical activity (odds ratios, 2.8–3.4). In addition, being white and having insurance were predictive of meeting the recommendation for moderate activity (2.8–3.0).

The analysts acknowledge that NHANES did not measure all potential confounders of physical activity or all possible types of physical activity. At the same time, they note that its measures of gestational age and of physical activity other than leisure activity, along with its short recall period, offer advantages over data sets used in similar studies in the past. “Given the benefits of…physical activity during pregnancy,” they write, “surveillance of these patterns and trends is appropriate.” If the relevant survey questions do not change over time, “these data could be used to -monitor trends and set national goals for physical activity among pregnant women.”—D. Hollander