Hi - I have had two pregnancies and put on 3-4 stone in each, but each time the baby was tiny - both born at 38 w, one was 5.5 lbs, the other was 6lbs. I did keep my bg's low throughout and lots of hypos - reckon I was injecting so much insulin that any sugar in my blood turned to fat in my body, not theirs! Either that or I just make em small. So don't assume you are having a big baby, I think that was true in the old days when bg's were less well controlled in diabetic mothers but if you're on top of the highs you may not.
In my second pregnancy my doctor kept trying to avoid any hypos, as you will know it can be either hypo or high when your pregnant as the middle ground is sooo hard to find, but I always said I didn't mind a few hypos so long as the baby was not exposed to high blood sugar, so I'd inject quite a lot and then eat a bit more when I was feeling low. Not saying this is the best way of doing things, as I did end up yo yo in g a lot, but I had two healthy babies so I must have done something right.
It is difficult, and you will probably find you need a lot more towards the end, I was injecting 30-40u with my meals and before lunchtime no matter how much I injected it would not bring it down (so I had to really restrict my carbs before lunch). So just be prepared for that. Good luck