Might this be because it's easier to sleep on your back if your fetus is small, and not the other way around?
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Super, one more thing to do wrong when pregnant.
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The thought of sleeping on my back while I was pregnant was just repulsive to me. My babies were already putting pressure on my arteries, so I couldn't stand that position. It made a C-section very uncomfortable for me.
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I remember as an eight year old girl going to the beach with my very pregnant aunt. She dug a belly-sized hole in the sand and lay on her stomach for a peaceful nap.
Later, when I was pregnant, I understood why. I have always been as stomach-sleeper, and every time my belly grew, I had to find different positions to sleep in. None were comfortable, but sleeping on my back was by far the worst!
Well, my problem disappeared each time after a few months, and I was not only overjoyed to have a new baby, but also to be able to sleep on my stomach again!
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@Sally I'm a stomach sleeper too, so I built what your aunt did except with pillows in my bed instead of sand on the beach. I had a pregnancy body pillow - the big long C-shaped one - and I would curl it around like a snake, with a hole in the middle, and put my belly in the hole, with other pillows next to the snake to even out my head and feet somewhat level with the snake. It was absolutely awesome! I also went to get a pregnancy massage once when I was 8 months pregnant, and was pleasantly surprised to find that they had special pregnancy cutout pads to put on top of the massage table, with the same idea - dense foam to lift the rest of your body up and a hole cut out for the belly, so you could get a proper back massage.
I didn't find sleeping on my back comfortable at all during pregnancy either. Especially in the later months, with all that weight down on top of me, I felt like I was gonna suffocate. I don't know how anybody manages to sleep like that.
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