If your Ob is talking 'big baby' I'm sorry she is NOT one of the good ones, she is obviously totally caught in the whole obstetric view that womens bodies are inherently incapable of birthing babies without intervention. It's a very bad sign, and if she thinks a scan is going to shed light on the situation, then I'd trust her even less.

Have you utilised a resource called 'The Pink Kit" ? It gives great info all about the pelvis and how it works in dynamic concert with bub during labour to facilitate birth, and gives great suggestions about how to optimise birthing positions etc.

The ONLY way to give a diagnosis of CPD is to labour, and see what happens...only in hindsight can you know.

That your Ob is so scared by SD casts aspersions on her ability, quite frankly, than anything else...

A 'big' baby does not mean a big head and shoulders necessarily, it can simply mean a heavy baby, so weight means nothing at all.

Babies heads are designed to mold for birth, and pelvises are stretchy structures desisned to facilitate birth.

I truly believe you can do this, don't be cowed by scaremongering.