My abdominal muscles have seperated too.
Congrats on being so far along in your pregnancy! You are getting into the home stretch!! What did your doctor say about measuring big? Babies do often develop at different rates in the womb and most of the time this is not a worry. Is your doctor following up with any other tests? They sometimes do that if you are more than three weeks outside of where they expect you to be in terms of measuring. Ultrasounds can be a pound off in the later part of pregnancy. Did they screen you for diabetes and you didn't have gestational diabetes, right? You may deliver early. Your due date may be off. Worst case scenario, a c section. But honestly, probably not. :>)) What did your doctor say about it?
Have you been tested for gestational diabetes? If so, and you don't have gestational diabetes, then you probably just have a big baby! Here's a bit more info about measuring large: https://www.stanfordchildrens.org/en/topic/default?id=large-for-gestational-age-lga-90-P02383
Has your doctor told you anything? Wondering about an update?