I remember going to a MW appointment at approx 36 weeks with my first & her asking if I had been having any braxton hicks yet, to which I replied "no". She then physically examined me for movements & measurements and pointed out that I was having braxton hicks there and then. I hadn't even noticed, I was expecting them to be painful but for me it was a very mild tightening around the bump. I then realised that I was having them very frequently, but still managed to be 9 days overdue with DD, so I don't think their presence is an indicator of oncoming labour.