Nomenclature

When two men get married and one takes the other's last name (rather than creating one of those hyphenated thingies), how do you refer to his former last name? JMG reader Vincent in Connecticut recently married and was amused that his partner's insurance form asked him for his "maiden name." Vincent says his partner's employer is open to suggestions. "Birth name" seems logical, but I have no idea how companies have been handling this. Anyone?