BHs were no indication of labour for me, though I had loads more BHs throughout the pgcy with each baby.
Ds1: kept being woken at about 1am by crampy backache from about 37w. One night, just before 40w, the backache didn't go away so I thought I'd try out the TENS machine. By 3am I realised that the backache was coming in distinct waves and getting more intense. Didn't stop until ds was born 48h later. Long, but perfectly endurable.
Dd: similar to ds1, but all through shorter - days instead of weeks of midnight backache, and just over 24h before dd born.
Ds2: completely different! Every evening, from about 40w, just as I was settling down to a bit of TV before bed, I'd start getting contractions. Irregular but uncomfortable, and they would go away when I got up and walked around. One night they suddenly turned into full-on contractions at midnight, and ds2 was born 2h later.
With all 3 my waters did not break until I was at the pushing stage.