I'm really curious if It is my birthday you'd say:
- Ñuhys sikagon(1) tubis issa. (sikagon = to give birth) or
- Ñuhys brōzio(2) tubis issa
(1): sikagon is the infinitive form of the verb, I don't really know how to adjectify-it; it might or might be not a correct way to use it
(2): brōzio tubis would literally mean (the) name day, expression that is a lot used in Game of Thrones; notice that brōzi is in the genitive singular case (whose day? that of the name) and it became brōzio.
This all depends on what traditions (if any) the Valyrians had surrounding birthdays. We don't know if they even celebrated them, or if they celebrated name days, or something else. However, I suspect "birth" would either be siknon or sittir. If you want to be really safe, you can always go with Kesys tubis nyke sittaks lȳs tubis issa. lit. "Today is the day I was born".
Peterson himself has in the past been reluctant to approach the subject: http://www.dothraki.com/2013/06/mhysa/#comment-2011