Eating plenty of carbs and sugar during pregnancy might put your child at greater risk of becoming obese in the future, according to a new observational study:
The American Journal of Clinical Nutrition: Associations of Maternal Macronutrient Intake During Pregnancy with Infant BMI Peak Characteristics and Childhood BMIThis study doesn't prove cause and effect, since it is merely based on statistical correlations. But it's still interesting. Note that the amounts of protein and fat that women ate during pregnancy were not associated with markers of future childhood obesity.
So if you want to err on the safe side, I'd recommend a diet based on real food, and low in sugar and refined carbohydrates.