While pregnant you only need about 300 more calories a day, but you need something like 10 times the nutrition. Taking prenatals is very important, but vitamins and nutrients are better absorbed through diet, and there are some combinations and substances they just can't make in the lab.
Remember everything you eat now has to go to keeping you healthy, pregnancy can be extreamly hard on your body, as well as give the baby a good start on life. Sugar does neither, but don't be to hard on yourself about pregnancy cravings
To stay out of ketosis eat mroe fresh fruits and veggies. Add in plain yogurt, granola, and some whole grains. You still need protien which is the building blocks of life, and fats which contribute to brain development. Your own fat stores are just energy and have already been depleted of nutrients, that is one reason they say not to lose weight while pregnant. You need the nutrients coming in fresh.
There is a book "A Mom to Be does Atkins" It's written by a doctor at the Atkins clinic who was pregnant with twins. It gives her daily menus and tips.
There is also peopl eon here who have done LC while pregnant. Find thier journals and see what they are eating and how they are managing.
Remember gaining a healthy amount of weight, not too much, means it will be easier to take off after. Regular exercise will also make the weight come off better, keep ab muscles strong which may stretch out, and help push oxygen to both you and baby.