I'm pretty sure you'll just know! For me, I got mildly painful contractions for a whole day. At that point I wasnt sure if it was the start of labour or what, but i though it could be considering I was 38.5 weeks.. then my waters just broke and I straight away got much more painful contraxtions 3 mins apart. At that time I definately knew. If you arent sure you can always come on here or ring your hospital and see what they think.