I started taking them quite a bit earlier, can't quite remember when, but may have been around 32 or 34 weeks. I started off with the tea and then worked up to the tablets and gradually increased the dose. From memory the tablets recommended dose is quite high (2 or 3 tablets 3 times a day) so it took me quite a few weeks to work up to it.

I do remember one day where I had upped my intake quite a bit and I had a lot of braxton hicks. I don't think that they would bring on labour, as others have said they are more about preparing your uterus than stimulating it... If I was you I would probably start taking them now and gradually build them up. I think it does take quite awhile for them to do there job, so if you leave it too late to start you don't get the full benefit iykwim...