Not a doctor, but I was just pregnant.

I don't think it's the ketosis itself so much as the fact that, while you're in ketosis, you're burning off fat and losing weight. Pregnancy is not the time to be losing weight. Even very overweight people are still advised to gain while pregnant (although they are told to keep the gain down, like 15 lbs. instead of the average 25-35). Your baby needs your fat stores. The baby also needs you to eat a healthy, nutrient-rich, varied diet. It seems to me that Atkins maintenance (with maybe a few added things like milk) would be perfect for this.

I ate like a pig in an ice cream shop <grin> for most of my pregnancy. I tried to eat "healthy" foods, but I didn't stop myself from eating a bunch of crap as well. I gained 42 lbs. My doctor told me that the pregnancy itself (baby, extra blood, extra breast tissue, etc.) weighs 26 lbs. on average. Anything you gain on top of that is just fat. Sure enough, I lost exactly 26 lbs. practically in the delivery room (okay, it was really within 3 weeks of birth). Now I'm here to take care of the rest.

I'm telling you this because I'd wager that if you followed a maintenance-level, healthy low-carb plan during your pregnancy your gain would be right around 26 lbs. That would make your post-partum rebound much easier than most people's.

My $0.02, sorry if it was too long.