Is it safe to diet during pregnancy?
I don't recommend it — pregnancy is not the time to diet. Normally, you should gain about 25 to 30 pounds during pregnancy. If you're overweight, you may want to shoot for the lower end of that range. The recommendation for women who are morbidly obese is to gain only 15 pounds. Some gain is inevitable given the weight of the baby, the enlarged uterus, the placenta, and the amniotic fluid. But that's weight that should disappear quickly once the baby is born. On average you should be getting about 2,500 calories a day (that's up from about 2,100 when you're not pregnant). You need those calories and your baby does, too. Plus, your physiology changes. Your blood sugar between meals drops to very low levels, which is why so many pregnant women have the feeling that they're starving and need to eat between meals. If you go into pregnancy thinking you need to lose weight, you'll find yourself incredibly hungry.
Babies are pretty efficient at getting what they need, so it's more a threat to your health than your baby's if you don't eat enough, but there's a risk that the baby will grow poorly if you're really malnourished.
My approach is to think of these eight months as part of a larger piece. Any weight you think you should lose, you probably put on during the years and decades before you got pregnant. So instead of trying to lose weight while you're pregnant, use this time to develop the healthy eating habits that will carry you through the rest of your life.