Today experts disagree on issues as important as proper weight gain, basic physiological adaptations of pregnancy, and the requirements for energy, protein, and micronutrients. Unfortunately, one unwanted side effect of this regime was small babies who bore an increased risk of death. Avoidance of excess weight gain remained the doctrine of practice until the 1960s, when it was observed that this restriction was often resulting in small babies bearing a higher death risk. Most doctors since that time have encouraged their patients to eat, and not to worry about extra weight gain. Now both mother and baby too often become too big, carrying an increased risk of death and of need for cesarean sections.
Big babies are harder to deliver and as a result, injury and death more likely.
Just proves you can't make something so wrong as the rich Western diet right by simply changing portion size. That's an extra 250 to 300 calories a day during the second and third trimesters. The simple carbohydrate glucose, derived originally from plant sources, is the primary metabolic fuel for the growing embryo, fetus and newborn immediately after delivery. Pregnant women become hungrier, especially during the last two trimesters of pregnancy. As a result they eat more food, taking in more calories and more of all the essential nutrients these foods should supply.