Doubtless the relevant medicos have already rendered some opinions re the relationship between your wife's back problems and.. the necesary pelvic muscles for delivery -- and just what sorts of strains could? might/will interact.
ie Seems a case where a Plan B would want to be sketched out pretty carefully: one of vastly greater competence than, say -
"Hey, I know ... let's start a Land War in Asia! But we'll wing it on what to do Afterwards."
Meanwhile - Luck! on Plan A, y'hear?
Ashton