Pregnancy & nightshift

Iv just found out by the company that I work for that they are changing our sleep overs to nightshifts, I'm just wondering if anyone knows if there are any policy's against pregnant women having to work nightshifts? I used to work full time nighshift 2 year ago and kept getting stomach infections and really bad heartburn because of it and bad stomachs because of my system being all messed up so god knows what this will be like when I am pregnant?! I love my job and really don't want to be pushed out of it because of this. Is there anyway I can get out of nighshift?