We will recruit a minimum of 18 pregnant women who may take part in 2 study days in both gestational stages, for a total of 72 study days. Potential participants will meet us for a preliminary assessment where we will evaluate their eligibility to participate in the study. The preliminary study will take approximately 1 hr during which we will examine body composition (bioelectrical impedance, skin-fold measurements, height and weight), resting energy expenditure (indirect calorimetry), blood glucose (glucometer), and medical history (questionnaire). Fasted blood glucose above 6.7 mmol/L is indicative of gestational diabetes. Participants with fasted blood glucose concentrations above 6.7 mmol/L will be referred to follow-up with their primary health care provider (see letter to physician).