I was a healthy weight and so far (week 28) Ive put on 1 stone. But don't think of it as weight. I read somewhere for a 7lb baby you put on 28-30lbs because of excess fluids, placenta, the fat needed for breastfeeding etc. If I put on 1lb a week now, thatll still only take me to 26lbs and baby is on track to be 9lbs!
It'll be what it is. I'm sure I'll lose it once baby is out.
Edited to add: I walk the dog miles every day, and my diet is 90% healthy. I have the odd chocolate treat, but I don't eat crisps, cake, biscuits and other junk. So I'm assuming the weight I've gained is baby and not me.