Gestational Diabetes is an ever increasingly common complication during pregnancy. In this situation, the best defense is a good offense. By following a high protein well rounded diet, such as The Brewer Medical Diet for Normal and High-Risk Pregnancy, it is often possible to avoid the pitfalls of gestational diabetes and pre-ecclampsia. This diet is not Atkins, it is not meant for weight loss.
I highly recommend the article by Henci Goer: Gestational Diabetes: The Emperor Has No Clothes.
Diet is the primary factor influencing gestational diabetes. Here are a few sites that will assist you in researching pregnancy diets.