What are the laws pertaining to unborn children and unresolved custody matters?

My pregnant ex (according to her family, I have not been able to speak with her directly) Fiance moved from Illinois to New Mewico to live with relatives after we lost our apartment. She is due at the end of March 2010 and is still able to travel within FAA Guidelines for pregnant women. Is there and sort of law that prohibits her from leaving the state under these conditions? And if so, is there a law that would require her to come back to the state of Illinois until such a time when matters of custody can be resolved?

Thank you in advance for your time.