Now i am just a mum to be in about 3 weeks BUT i read a magazine all about pregnancies (it was called Bumps or something like that, it was written by doctors i think i read on the cover) while waiting for my last dr's appointment & there was a BIG section on all the myths & which ones weren't exactly true.
Here's what i read :- there is no medical PROOF that says laying on your back will harm the baby or your internals so i'd say, if you cant lay on your tummy & your side hurts too much - definitely lay on your back. I have been for most of my pregnancy & nothing has happened (i get uncomfy occasionally depending on how bub is laying but that's it), bub is normal size, active, healthy & i'm healthy according to all the tests so nothing is wrong there.
Anyway, so, i'd go ahead & sleep on your back if you can get comfy like that coz if the medical world call it a myth then chances are it is!
Hope that helps you out a little & good luck with the rest of your pregnancy!
Kel, SA, Mum to Lillian Rose - 06/06/06