IME, it runs true to size and is often the brand people use to judge whether other brands run small or large. DD was 8lb 1oz, she could wear Carters NB size for a few weeks, but wore the 3mo size until 3mo, the 6mo size to 6mo, etc. By 3mo she was 97%tile for height and 80%tile for weight and stayed there, so the clothes should fit a larger baby just fine.
Take back any Gerber stuff you've got - DD outgrew the 0-3 Gerbers at 6 weeks and the 3-9mo stuff by 4mo.
I found with my son that it ran big. Something to think about though is just because you may have a big baby at birth he may not be big as he grows. My DS was 8lbs 7oz born at 37 weeks and ended up being on the smaller side as he went on. He's on the taller side now but when he was an infant newborn-1 yr he was fairly small.
It may run a little big, if you go by the weights on the tag. It say 8 1/2 to12 1/2 lbs and DD was swimming in it until she hit around 9 lbs. My DD is long and lean though, so it may fit differently on a baby that is a little chubbier through the middle. DD wore newborn clothes until about 5 or 6 weeks. She is still fitting her 0-3 well now and is 10 weeks and around 11 lbs. Like PPer said, Gerber onesies run small. They are the only 3-6 mo clothes that DD is currently wearing. If you expect to have a big baby, I wouldn't buy any NB clothes, but you should be fine with 0-3 for a while.
Re: Does Carters stuff run big or small?
IME, it runs true to size and is often the brand people use to judge whether other brands run small or large. DD was 8lb 1oz, she could wear Carters NB size for a few weeks, but wore the 3mo size until 3mo, the 6mo size to 6mo, etc. By 3mo she was 97%tile for height and 80%tile for weight and stayed there, so the clothes should fit a larger baby just fine.
Take back any Gerber stuff you've got - DD outgrew the 0-3 Gerbers at 6 weeks and the 3-9mo stuff by 4mo.
They look like they run big compared to Gerber..
This exactly!