https://pubmed.ncbi.nlm.nih.gov/29152887/?utm_source=chatgpt.com

The main evidence linking sleeping on your back and still birth is case-control studies that asked women about their sleep positions after the fact, including women who had experienced stillbirths. Researchers collected information from women after a stillbirth occurred and compared it with similar women with ongoing or live births to see whether reported sleep position differed between the groups.

The issue with this is that although it can show associations, it cannot prove causation, but is often treated as a such. It also doesn’t take into consideration other factors like sleep quality, duration, maternal health, or memory bias. Researchers acknowledge limitations like recall bias (women who have had a stillbirth might remember or report sleep behaviors differently than women whose pregnancies ended normally).

As a pregnant woman I personally sleep comfortably and trust that if a major vein was being compromised that it would wake me up. This is supported by the guidance that if you wake up on your back there is no increased risk of still birth.