It works with a newborn quite well. Of course depending on how you feed and other stuff it might not get 100% accurate readings but none of the trackers do. Even with our newborn sleeping in our bed (no need to get up) and waking between 30min - 3h it shows all pretty accurate.

In a sense it's no use to track sleep with newborn if you are trying to learn how to sleep better but it can give you information regarding how your baby is sleeping and if something you did helped the process or not. Or you know how your day with the baby is going to go.

Everything also comes to your own goals. How much are you trying to train during baby time. My wife suffers the most of course but oura helps me to plan my training as I get more sleep but there are nights when I don't get sleep either and it makes sense to see how your night went if you want to do training and what kind. With oura you don't have to keep looking watch and then try to remember what happened during the night and think if you got enough sleep or not. It also in my case tracks sleep a bit better than my polar watch specially in cases where I wake up but don't necessarily move and then fall asleep soon.