I think it's 26 weeks when they suggest you start Sarah, but some of it you could do now / sooner for sure, then you are well familiar with it later. I find the mapping of the pelvis to be fascinating, learning which of the four main structures you have. Don't try and do it all at once at the last minute! Its too much to take in. There is an additional VBAC component but I haven't seen it yet, would be interesting.