I since Sunday have two big headed children and have had two emergency sections - however I don't believe on it's own a big head equals c-section. With my first I knew she was big an likely with big head due to size of DH when born, but I never considered I might end up with section - just believed my body would take care of it. In the end DD had other ideas, posterior brow presentation got stuck so cervix stopped dilating and just started swelling, so ended up e csection (head 35 weight 4.12 kg). With my son I decided that would like VBAC but was prepared that might end in e section. I knew his head circa was big but was hoping he would be in better position so wouldn't matter. In the end he decided to copy his sister although I got a few cm further dilated he got into posterior position and jammed his head, cervix stopped dilated started swelling etc (maybe something about shape of my uterus and shape of head leads to the problematic positioning - who knows). So had e-csection again, which was a good experience and because I had already entertained the possibility and thought about what scenarios I would be happy to go to csection for it made it very easy to accept and be happy with.

So no big head I don't believe equals section, there are lots of factors that come into play, and you will never know how will work for you and you on that occasion, so don't dwell on it at all.