In my antenatal class we were taught not to actively push but to relax our lower jaw so and breathe out so that we weren't getting in the way of our body pushing the baby out by itself. Definitely no chin to chest trying to push a melon out of our bums!
Having far too much time on my hands during maternity leave, I've been watching One Born Every Minute, The Midwives etc. and every single birth on those programmes has shown the midwives telling the woman in labour to put her chin to her chest and push really hard. With DC1 I was told to do the same thing. He ended up getting pulled out by a ventouse but that's probably due to me point-blank refusing to let anyone stop topping up the epidural...
So, any ideas on the reasons behind the two techniques? Does chin to chest really tense all the muscles and work against the pushing contractions?