For the study, Evenson and Fang Wen, a programmer in the public health school's epidemiology department, used data from the National Health and Nutrition Examination Survey collected between 1999 and 2006. The data included interviews with 1,280 pregnant women aged 16 or older. The questionnaire defined moderate intensity activities as tasks that caused light sweating or a slight to moderate increase in breathing or heart rate, and vigorous intensity as activities that caused heavy sweating or large increases in breathing or heart rate.

The proportion of women who were active enough to meet the guidelines' recommendations was about 23 percent.

The national survey also showed 23 percent of women reported getting some activity going to and from work or school; 54 percent got moderate to vigorous household activity; and 57 percent reported moderate to vigorous leisure activity within a month before the interview. Moderate to vigorous leisure time activity was significantly greater among women in the first trimester compared to third trimester.

SOURCE University of North Carolina at Chapel Hill