My baby turned breech at 37 wks, vertex at 38 wks, breech and then vertex again at 39 wks, so they can spin around any old time!!! She is vertex (head down) still as of today, so we are hoping she STAYS that way!
I wouldn't worry about a breech birth as much as I would focus on getting a breech baby to turn!!! I've been using a chiropractor to get my spinner to turn with AMAZING success (the last time she turned it was ONE HOUR after I had left the chiro office!). My chiro says she likes to start with breeches at around 34 weeks, to give them plenty of time to get head down (the chiro technique is called the Webster technique, so you can do some research on who in your area might be able to do it if you want).
So, my advice is this: if baby's still breech at 34 weeks, call a chiropractor experienced in the Webster technique.
In my area there is only ONE OB who will deliver a breech baby vaginally; everyone else send you to surgery immediately. So, put some focus on turning that baby.
Sending you good baby-turning vibes!