Accurately measuring pregnancy physical activity is critical to assess the percentage of pregnant women meeting the American College of Obstetricians and Gynecologists (ACOG) guidelines. In addition, valid assessment of pregnancy physical activity is important for epidemiologic studies assessing the relationship between physical activity and maternal and fetal health outcomes. Currently, population-based surveys designed to measure compliance with these guidelines tend to rely on metabolic equivalent (MET) intensity estimates for household tasks provided in the Compendium of Physical Activities. However, these MET intensity estimates are available only for nonpregnant adults and are not intended for adults with conditions that would significantly alter their mechanical or metabolic efficiency, such as pregnancy. In addition, due to the physiologic changes that occur throughout pregnancy, energy expenditure required for specific activities may vary over the gestation period. Therefore, relying on MET intensity values published in the compendium may lead to attenuations in observed associations between physical activity during pregnancy and maternal/fetal outcomes. To the authors' knowledge, prior studies have not measured MET values for household tasks among pregnant women. Therefore, this study's primary aim is to measure the metabolic cost of four commonly reported household activities (window washing, dusting, vacuuming, and laundry) during each trimester of pregnancy. Secondary goals are to: (a) assess if energy costs for these activities changed across trimesters; and (b) compare their observed values to those presented in the compendium. (Contains 2 tables.)