Big heads here to. My cousin had a 40cm head and my aunt birthed viginally. My DH, my brothers and me had between a 36-38cm heads. All vaginally. We are all 8 pound babies. If it rubs in the family maybe share your concerns with your doc and discuss options with them. When I fell pregnant we discussed this with our doc who understood that I was worried bout a big bubba. In the end I had a premmie bub, so my worry was the opposite.

Now our dd has a hc way above the 97th percentile line.

Talk to your doc about your concerns.