Sleeping on your stomach or laying on your stomach during the early stages of pregnancy are fine and will do no harm to the unborn baby.
But as you get further into your pregnancy and as your belly grows bigger and bigger it will be uncomfortable to lay on your stomach or sleep on your stomach.
Although it's unlikely to harm your baby laying on your stomach or sleeping on your stomach when you're pregnant it's not a good idea either.
I would not want to risk the potential of harming my unborn baby by laying on my stomach because the baby inside your stomach is so precious that you don't want to do anything that could harm them.
The way your stomach is designed and the womb is designed to protect the baby it's considered safe to sleep on your stomach while pregnant or lay on your stomach while pregnant but for me it's not worth the risk.
I always just laid on my side or back when I was pregnant because I didn't want to risk harming my baby even though my doctor said it was considered to be safe.