Cactus,
Logically, head diameter should be 90+mm or 9+cm, otherwise why else would we need our cervix to dilate to 10cm to fit baby's head? It would then make sense for head circumference to measure 31-35cm. If our baby's head diameter at birth was only 3.5cm, it would be extremely small, don't you think?
Anyway, I'm still waiting for labour despite losing mucus plug last Mon and having lots of BHCs. EDD on Sat, hopefully cervix will be ready by then. Kinda knew deep down that my #2 would be like #1, late or at best, on time. Wait until v sian, after 4 days HL at home, insisted on coming back to work this week. Only thing to give thanks for is that her weight caught up v fast in the last 3-4 weeks. Went from 2.1kg at 36 weeks to 3.1kg at 39.5 weeks. Wonder if she purposely stayed longer inside me to prove the gynae wrong, because he said he didn't expect her to exceed 3kg at birth and kept comparing her weight to #1, who was 3.5kg at birth.