For a birthday with an 0 (i have one in July) I would take a day off the diet. And I'm not someone who advocates taking days off. Usually i feel like I can wait and do something when I'm at goal, but you only get an 0 birthday once a decade.
Take a day off, go crazy if you want to, just don't let it become a week off. Have your meals for the day after already in the fridge and hand out any cake or treats among your friends on the day. I've fallen off diets totally before through coming off on my birthday, but it -is- manageable.