I would go word-for-word, since 'mother's maiden name' does make sense, but only most of the times, not always: it could be the case that the mother was given/took a last name different from that of her father. And after all, they didn't ask about שם נעורים של האם, which they certainly could:
http://www.google.com/search?hl=en&q="שם נעורים של האם"&aq=f...