It's all about the positioning and the size of the head!!!
DS was 9lb $ and my first. The labour was only 4 hours long (which I really think was down to his size and the fact I'd been having bad braxton hicks for weeks before) but he got stuck in the birth canal for an hour during the pushing stage.
After some intervention he did eventually squeeze his way into the world, with difficulty. Turns out his head measurement was similar to that of the average one month old 