And preggers people only need to gain 20% of their weight (if they start at human size). So a 150 lb woman should not gain more than 30 lbs. A small person could only need to gain 20 lbs. Women who take it as an excuse to gain 60-70 lbs are abusing their bodies.  Because babies are 5-10 lbs, placenta and water is around 5-7, rest is extra padding for baby safety. And boobies.