I take the high prevalence of these conditions as evidence that pregnant women are generally malnourished and the need for micronutrition stimulates appetite, causing women to gain weight and / or develop gestational diabetes.
The protein / carbohydrate / fat / fluid / micronutrition requirements for a 155 lb endurance athlete in the midst of marathon training vs. a 225 lb bodybuilder recovering from a heavy resistance - training session are quite different.