I was about 20 lbs overweight and gained 25 lbs with my first child. I lost 29 lbs between giving birth and leaving the hospital. My doctor didn't think there was anything wrong with it. In fact, over the next few months (while breast-feeding my son) I lost down to 25 lbs below my pre-pregnant weight. My doctor was very happy with the weight loss.
One of the things about breast-feeding is that it allows you to eat a little more (healthy foods), but still lose weight. Our bodies are designed that way.
Of course, with my second baby, everything changed.