With DD my fundal height measured on average at every check up and she was born at 38 + 2 and weighed 3.12kgs (7lb), I only put on 6kg's for that pregnancy.

Obviously the twins are a bit different as they are generally smaller babies anyway, but they were born at 37 + 4 and weighed 2.63kg's (5lb 8oz) and 2.77kg's (6lb 1oz) and my Ob was very happy with the weights, I only put on 13kg's for that pregnancy.

DH was over 8lb when he was born and I was 7lb 3oz born 4 weeks early so I always thought I would have 'chubby' babies but I had skinny one's but they have made up for that now with all 3 being in the 50th to 75th percentile for both weight and height for there ages.

Maybe bubs has already started descending or is preferring to stay curled up at this stage.