Energy requirements of pregnancy.

The energy requirements of pregnancy is a topic of considerable uncertainty because the apparent energy costs--to supply the energy required for the changes in maternal and fetal tissues and to cover the increase in BMR (basal metabolic rate), amounting to the equivalent of an extra 250-300 kcal/d--are rarely paralleled by actual findings. However few studies have investigated this problem in a controlled, longitudinal, and statistically acceptable fashion. In the present study, measurements of energy intake, BMR, body weight and fatness, physical activity, and mechanical efficiency of movement, were made on 162 women in Scotland at 2 to 4 weekly intervals throughout pregnancy and data from 98 of these women were also obtained in the pre-pregnant state. Data from a parallel study in Holland are also given. The gains in body weight, fatness, the fetal and placental weights, and the increase in BMR were all at the normal expected values. However, increases in energy intake were of the order of only 100 kcal/d during the second and third trimesters. Comparatively small reductions in physical activity, which would be very difficult to measure precisely, are described which could account for the difference between actual energy intakes and the energy costs of pregnancy.