For most women their OB/GYN is also their primary care physician. OP can bring up his concerns and if her doctor thinks the cause of her recent lack of impulse control is something other than pregnancy hormones then her doctor can refer her to a specialist. Her doctor could be another voice suggesting counseling, and may also want to monitor OP's wife more closely for post partem depression after she gives birth.
If the OP's wife does have an undiagnosed mental disorder then he would have an easier time co-parenting for the next 18 years after the divorce if she was being treated and acting rationally.