Your right that more calories are needed. Damm, I hate the internet. I'm talking about the women who are told that they will require roughly 3,000 calories a day. They take it to mean they can eat whatever they want and end up consuming say 6,000 calories a day.
I have actually seen this happen out here. At least 2 girls I know of took being pregnant as a free pass. They ate everything and gained a hell of alot of weight, trust me I say it wasn't all baby weight. In fact one child has a health condition related to mommies eating habits.
Too much weight gain above and beyond the needs of the mother and the developing baby can result in serious things such as gestational diabetes, high blood pressure, difficult delivery and more weight to loose after the baby is born. So too little is not good and neither is too much….once again as enduramil says it's all about balance.
I'd think every pregnant should see a dietitian or nutritionist if they can since doctors don't have time to provide nutrition advice…so good you recommended your client to see one.
If you are a healthy weight before pregnancy the recommended weight gain ranges between 11.5-16 kg or 25-35 lbs.