it depends on the name i suppose, a little nickname fair enough, but at 12wks and hes referiing to it as either a girl or boys name, hes gonna be dissapointed if it aint what he thought, especially with him naming bump it gives him more of a bond.
but we were always set on my sons name, and i 'felt' my son was a boy from early on and my scan proved that right anyway, although we never referred to him as his name, it was baby or beanie as the odd times i did call him by his name while expecting it made me feel like i was talking about someone who had passed away

and i didnt like the idea.
id let your fella call it what he wants so long as he aint gonna be too disapointed in its outcome, at the end of the day, hes showing an interest, some men dont!