I've read that in the second tri the normal weight gain is 2.5kg per month then in the last tri the baby should put on 250g a week but we should be gaining less than a kg per month as we're no longer gaining the extra blood volume etc. I was really happy to see I had lost a bit of weight in the last two weeks as I had put on a lot of mummy weight over holidays. I'm sure that as long as they are happy with bub's growth you should be fine.