I've just seen this and was going to say pretty much what Old Geezer said.
However, I got married in my late 30's and didn't have my two children until I was 32 and 35, thanks to lots of tests, fertility drugs and 'getting in on'!
It is riskier, may take longer to conceive, very tiring and there will be a few older Mum's at the school gates. If having another child at 40 is what you and your husband really want, I wish you lots of luck.