I can't answer how bad it is for the baby, my advice would be to ask your doctor. But I do have the same problem with waking up on my back so I started putting a pillow behind me which seems to work.
During the first trimester it is fine but after 16 weeks, the weight of your uterus weighs on a major artery that returns blood to your heart. That being said it can very much interfere with the blood flow and nutrients to your baby.
It's a bigger problem for women with high blood pressure, or diabetes.
If your having a hard time sleeping on your side, try putting a pillow between your legs or even try a pregnancy pillow.
As long as you are comfortable it is fine imo. I'm not a doctor, but this is something I've never worried about because if your body is uncomfortable you will change position.
This is my third time around and I can say with both previous and this one I've slept on my back. I start on my sides but usually end up on my back. I don't think you need to be terrified. Talk to your doctor about it if it really concerns you.
I start on my side and end up on my back, which is ironic seeing as I've never been a back sleeper. I think I end up there because I have CTS and my hands and arms go numb if I lay on my sides. I'm not too concerned because as @tdart14, I think if I'm uncomfortable I will move.
As long as you are comfortable it is fine imo. I'm not a doctor, but this is something I've never worried about because if your body is uncomfortable you will change position.
This is exactly what two different OB's have told me. And the more I read about it, it seems like most studies on back sleeping in later pregnancy support the theory that it is only dangerous for a very small percentage of women. But like most things pregnancy related, it seems to have become a catch-all recommendation to expecting women. More info:
Of course (with everything) there is always a counter study that says the opposite, which is why it is important to do your own research. Emily Oster also covers the back sleeping thing in "Expecting Better", that has been a good reference for me this pregnancy.
Lying on your back puts pressure on your inferior vena cava, which can cut off oxygen to your uterus. Please note, however, this is when you're FLAT on your back and not moving, so if, let's say you sleep on your back with one of your legs bent, it's unlikely that you're in the unsafe position. Also, as pps have mentioned, you will have trouble breathing and get uncomfortable before it's actually causing any major harm. I'm a back sleeper too and have been trying to switch to a side sleeper and it's not easy. Pillows help, especially body pillows and pregnancy pillows. You can also try putting a small pillow or wedge under your right hip to ensure you don't end up flat on your back.
Long story short, don't worry TOO much, your comfort is really the most important thing while sleeping. If you're comfortable, it's unlikely your body will let you do anything to harm your baby in this way.
I've woken up on my back a few times, and I wouldn't stress it too much. As with any medical question, you really should discuss it with your OB, but from what I've read you would start to feel uncomfortable before any damage is actually done. I doubt you sleep flat on your back, vampire-style, anyway.
I'm also not much of a back sleeper but I find myself waking up on my back in the early morning.. It's more of a half-side twist thing because I surround myself with pillows. I don't stress much about it, either.
Like PPs mentioned, I've read it can be dangerous to sleep on your back during the second tri. I use my Snoogle body pillow to sleep on my side and find it to be very comfortable!
My fiancé spoons me most of the night while I hug a body pillow in between my legs. I love sleeping on my back and stomach but it's way too uncomfortable now. It's kind of like I'm sandwhiched in between him and the pillow and it's almost impossible to roll over in my sleep lol.
I had this problem so I ask about it and the doctor said as long as I'm comfortable and I can still feel my legs that everything is fine... so if I we're you I wouldn't worry but if you are still worried about it you can get the opinion of your doctor. Hope this helps god luck.
Re: sleeping on back??
It's a bigger problem for women with high blood pressure, or diabetes.
If your having a hard time sleeping on your side, try putting a pillow between your legs or even try a pregnancy pillow.