Hi. My 18 week LO moves herself into a side sleep position even when I lay her down on her back. She sleeps in a baby sleeping bag. She uses the bed rails to hold her body in place. She knows how to roll onto her tummy but doesnt do this in her sleep because she still dislikes tummy time, and doesnt have a huge amount of head strength or can’t move her arms easily in this position. She will get upset if she goes into the tummy position. Ive attempted to put her on her back from the side position but this wakes her up, and she then just puts herself back there. Im giving extra tummy time during the day to build her strength. We are adhering to all of the other safety measures (firm mattress, room sharing, no soft items in cot etc). Can I leave her in this side position that she puts herself in even though there is a risk she will go onto the tummy (with not a huge amount of upper head / neck strength yet). Thanks in advance and have a great weekend. Your site is extremely valuable to parents.

What you are describing is not unusual at 18 weeks.
It is normal & not something that needs to be stopped - it is about providing a “safe as is possible” environment in this new stage.
Most babies will be rolling by 4 - 5mths & some prefer to sleep on side rather than tummy or back.

**Are you using a sleeping bag with arms out? - ie not a swaddle suit.

Red Nose has the following information now that your baby is starting to roll.

Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

As babies grow and develop they become very active and learn to roll around the cot.
At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
By this stage it is not necessary to wake during the night to turn baby over to the back position

Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over