A pregnancy doesn't have to make a male character effeminate persé. It could make him more sensitive and more domestic but that doesn't equate effeminate necessarily. Perhaps you can compare it with a man who is preparing for a sexchange. With the intake of 'female' hormones he changes, in body and mind. I am sure these changes are documentated and accessible. Perhaps it is an idea to read about it a bit and see if it can help you write within the boundaries of realism. As far as mpreg is realistic ofcourse....