I would also suggest that rather than going 'low carb' during pregancy and risking getting an imbalanced diet and possible malnutrition problems, you follow deleting's example of a Low GI or 'good carb' way of eating. Carbohydrates provide a lot of important energy and nutrition and, if you make intelligent choices rather than trying to eliminate them, they will serve you very well and keep you in good health.
If you need to lose weight post-pregnancy, a Low GI based diet combined with some portion/calorie control and increased exercise should be very effective.