This isn't something you can change, but my mum is a midwife, and she and all the other nurses say they see it all the time.

Whenever there are thunderstorms, it causes women to go into labour.. Something about the change in baromic pressure? I know for me (i was overdue anyway), that there were thunderstorms Sat night and Sunday day, but Sunday night i started having contractions... And the hospital was so full when we got there we had the spare labour room.

I mentioned it to the midwife on duty also, and she also says that they see heaps more women after thunderstorms.