Abena Sizing

I already blogged about this but figured I could get some more responses in a thread. I have an opportunity to order some diapers online when I order a birthday gift for my mother. I was looking at the Abena Abri-Form but am unsure if I need medium or large. I have about a 41-42 inch waist and 51 inch hips, putting me, waist-wise, at the far end of medium's size range and the low end of large's. I've tried large Bambinos, and found them too big.

Abena Sizing