Basal metabolic rate (BMR) is one of the major components of total energy expenditure (TEE). It is affected by various factors, such as body weight, body composition, age, race/ethnicity, gender, biochemical parameters, physical activity, and health status. Gestational diabetes mellitus (GDM) is the most common metabolic disorder during pregnancy and it increases the risk for health complications, such as stillbirth, diabetes mellitus, and cardiovascular disease in later life. Both BMR and GDM have been linked with gestational weight gain (GWG), a fact suggesting a possible association between them. However, assessing BMR is a complex procedure, which becomes more complicated when additional parameters, such as pregnancy and GDM, are taken into consideration. The present review summarizes the current knowledge on factors affecting BMR and its regulation in relation to pregnancy and GDM. Future research addressing these associations should thoroughly consider other factors that affect BMI when designing such studies and/or discussing the BMR outcome results.