i just had my baby 2 wks ago. i slept on my stomach for as long as it was comfortable.. when it gets un-comfy, stop. But also remember that even after you stop sleeping on your tummy, it is dangerous to sleep on your back also. When you start to get a larger stomach, it makes it hard for the baby to breathe when you sleep flat on your back. Try to sleep with a pillow propped up under your side to help you sleep at an angle, later in pregnancy. My doc's & nurses always said the best sleeping position, if possible, is on your left side.. allowing your lil one to breathe efficiently.
i haven't intentionally slept on my stomach since week 15. i made the mistake of telling my fiance that one of my books said to switch sleeping positions during week 15 so he flips out if i do. as for the back, i believe (during weeks 15 and on) that the baby is large enough to where he or she puts pressure/weight on the vena cava (i think?) which can result in him or her not getting appropriate blood flow, etc.
we're 23 weeks into the pregnancy right now, and the majority of the time i sleep on my left side (because it's more comfortable than the right) but it's starting to become restless anyways!
I have been trying to sleep on my left or right side since I found out I was preg at 4 weeks. I started so soon because I knew it would be hard to stop sleeping on my stomach. Besides, it helps blood flow to the baby if you sleep on the left side, and I am trying to do as much as I possibly can to have a health pregnancy.
Angel Baby: December 28, 2007
Liam: December 8, 2008
David & Abby: December 8, 2010