Surprisingly, sleeping on your stomach is fine as long as it feels OK.
Early in pregnancy, your little one is tucked way down in the uterus in your pelvis. As the uterus grows, the top (fundus) moves above the pubic bone, and you may be able to feel a little lump there. Still, the baby is inside the muscular uterus and protected. You may not even feel the lump when you lie on your tummy. As your baby continues to grow, the uterus grows and stretches, reaching the level of your belly button at around 20 weeks. Mid-pregnancy, most moms-to-be start to find it uncomfortable to lie on the “bump.” But if it feels OK, it won’t hurt the baby! She is in a warm water balloon inside a muscular uterine shell. As you and your baby-to-be continue to grow, the uterus gets bigger and its walls get thinner, but even at 9 months, the walls of the uterus offer quite a bit of protection.
So this is one case where listening to your body works really well—as long as it is comfortable, feel free to sleep on your tummy without worry! You will know when it is time to change it up.