Is dieting while pregnant good for the baby?

It is better just to eat healthy, calorie count, and excersise.  Your baby needs everything that it can get under a normal diet, but unless your doctor tells you otherwise it is always safe to eat healthy and excersise.  It will also cause you to lose weight and keep it off better then any diet.

 I second the advice of smcharlton.  Unless your doctor recommends that you go on a diet, it is best to maintain some form of exercise and eat a healthy, well balanced diet during pregnancy.  Many overweight women don't really gain much weight during pregnancy because they have extra stores that the baby takes from anyway, but maintaining a healthy lifestyle and habits is the best for both mom and baby.

I also agree with smcharlton. Most doctors won't recommend you go on any type of diet because of the harm you can potentially do to yourself and you baby. If you plan on starting a new exercise program talk to your doctor first. As far as your diet just making healthy food choices will benefit  you and your baby's health more than just losing weight.

It's never a good idea to try to lose weight while pregnant.  It is a good idea, though, to eat healthily and get plenty of exercise.  This will keep you from gaining too much weight, and make it easier to lose what you do gain.