Honestly this is not worth expending too much mental energy on. There is a weak link between sleeping flat on your back in the third trimester only and stillbirth, but it's likely that the link is the other way round, I.e. women who have conditions predisposing them to stillbirth happen to be more likely to sleep on their backs. You will know if lying on your back is pressing on a major vein because YOU will get dizzy and shift position. So if it feels ok, you can do it.
As pp have said - don't worry too much about it. Besides, small periods on your back such as in the bath etc are very unlikely to have an effect. I had to keep lying on my back in 3rd trimester as I had such bad rib pain - that was the only position that would provide any relief! I'd lie down for half an hour or so to get rid of the pain. My 12 day old son seems unaffected by it
I sleep where I can. TBH I think there is a lot of b*llocks on 'which side to sleep on' and it's yet another thing to make us mums worry!!! I sleep on the left where I can but naturally wind up moving around a lot - as my mum pointed out, she slept where she could wth myself and my brother and we really pretty ok (and both 6 foot and over!!).
The week I tried a pregnancy pillow I wound up spread eagled, on my back like some kind of beached whale 🐳😂
I think don't panic about it and do what you can chick. Do you have the study handy? I suspect there'll be some kind of caveat to it or a recommended period of time when to commence not lying on back. I'd imagine you can't comfortably past a certain time-24 weeks and getting there myself!
I actually spoke to my midwife about this at my 16 week appointment because I keep rolling over onto my back. Propping a pillow behind me doesn't help at all as I seem to just shove it out the way in my sleep. Anyway, apparently it's fine. As others have said, later on, the weight of baby can press down but this is only a problem if it causes you any discomfort (i.e dizziness and feeling faint). I've now taken to sleeping however is most comfortable as sleep is far more important for the health of my baby than not sleeping on my back. I think we should all try not to worry
I remember reading that study when it was mentioned in my last pregnancy.... From what I remember there were some questionable methodological concerns (I review journal articles from time to time, so this is my jam).
The article asked the women after they had experienced a stillbirth which side they slept on the night prior to the birth of their child. Is that a reliable self report given that the women interviewed had just been through a signifiant trauma? I'm not sure.....