It's not a breathing technique as such, but I do think it really works,
once you are in the land of the serious contraction, at the start of each one recite a nursery rhyme or similar (I went for in my head only and 'Nellie the Elephant')
I fould this gave me a lot of focus and control, as I knew each contraction would follow this pattern
Nellie the elephant packed her bag and trundled off to the circus
Off she went with a trumpetty trump
Trump, trump, trump pain ok
Nellie the elephant packed her bag and trundled off to the circus
Off she went with a trumpetty trump
Trump, trump, trump pain building up
Nellie the elephant packed her bag and trundled off to the circus
Off she went with a trumpetty trump
Trump, trump, trump pain unbearable
Nellie the elephant packed her bag and trundled off to the circus
Off she went with a trumpetty trump
Trump, trump, trump pain easing off
Nellie the elephant packed her bag and trundled off to the circus
Off she went with a trumpetty trump
Trump, trump, trump pain pretty much gone, breath and collapse
That said I cannot bear to hear sodding Nellie now and in fact even typing it has made me feel a bit queasy.
But it is a much better teqnique than counting imo.
Hth and good luck.