Fundal height is notoriously inacurate, to the point where many caregivers (both ob's and midwives) don't measure it anymore.

If you are measuring so far out of whack, my advice would be to refuse any more measurements. All it's going to lead to is more hand wringing on the part of your CP's for no good reason...which is going to lead to more tests and interventions for you.

If your abs are separating anyway this will be the case even more so.