It may start labour, but would you have had a fast labour anyway? We'll never know

But I have heard it from the horse's mouth (an Ob) who admitted there is no proof it speeds up labour and that it's just what they 'think' (his words).

But I do know it can cause problems more than it it has benefits - not only infection, but cord prolapse if the baby is high, posterior babies seem harder to move once waters have broken, you are put on the clock having artifically ruptured membranes, you have to stay in hospital and they will get your labour going one way or the other, if you have a posterior baby and have a premature urge to push it just makes it worse (my poor sister) .... so many reasons to leave well alone! Membranes left alone often break just before pushing and I think this serves a good purpose.