Since the nineties they started advise parents that all infants should sleep on the back, which reduced SIDS a lot [0]. But it means that it is is very hard to draw any conclusions at all about other factors.
Not in all countries. In my country we lay them on their side supported by a rolled towel. We make sure they equally lay on both sides. Sleeping on the back will give them a flat head.
> Sleeping on the back will give them a flat head.
I'm fairly certain this isn't true. I would expect there to be a lot more flat-headed babies and people around. I don't think I've ever seen one. Not telling you what to do, just pointing out I don't think that part is factual.
It’s certainly true. Our oldest kid had a quite flat head when he was an infant, so we had to get him a special pillow and was advised to try to let him sleep on the side. But it’s nothing that you think about except when you put your hand on the back of his head, and most of it will allegedly disappear when the scull grows.
And if you think my anecdote is enough, Google will provide you with plenty, e.g., [0].
If you look around you will start noticing it. A babies skull isn't even fused and has soft spots (fontanelle) so it makes perfect sense that it can be shaped and molded as it develops and grows.
[0] https://safetosleep.nichd.nih.gov/research/science/backsleep...