Basal metabolic rate and work energy expenditure of mature, pregnant women.

Resting and working metabolic rates and physical fitness of twenty-one mature women were studied at various intervals during the last half of pregnance and in sixteen of them again eight to twelve weeks postpartum. Basal rate (BMR) was increased more than body weight during pregnancy, and there was a small drop in BMR per unit body mass near term. Data on lean body mass (40K) suggest that the small terminal fall in BMR is not explained by a shift in body composition toward increased fat or water. The increase in energy cost of work paralleled the gain in body weight during preganacy. Net energetic efficiency thus appeared to be higher for work performed during pregnancy, if recovery rates are assumed to be uniform. However, according to their heart rate reponses to fixed hard work, the women were less fit during pregnancy than they were postpartum, with the level of fitness decreasing as pregnancy advanced. The prolonged rate of recovery suggests that oxygen uptake may be increased for a longer period after work in the pregnant woman. If this is true, energy expenditure will be seriously underestimated by the application of energy cost figures obtained in the conventional manner.