Newborns frequently curl onto their sides when placed on a flat surface, and it’s almost always caused by a normal reflex leftover from the womb. The behavior typically disappears on its own within a few weeks. In the meantime, the safest approach is to keep placing your baby on their back every time, on a firm mattress with nothing else in the sleep space, and gently reposition them if they curl to the side.
Why Newborns Curl Onto Their Side
During the last couple of months of pregnancy, a baby’s muscles strengthen and tighten into the fetal position. By the time they’re born, full-term newborns have a strong involuntary flexion: arms bent, legs pulled toward the belly, hands curled into fists. When you lay them down on a flat surface, those same muscles can contract and pull them onto their side.
This is called the newborn curl, and it’s actually a sign of healthy muscle tone in a full-term baby. It’s not the same as intentional rolling, which doesn’t develop until months later. The curl is reflexive, not voluntary, and it typically fades after several weeks as your baby’s muscles relax and adapt to life outside the womb.
Why Side Sleeping Is a Concern
The American Academy of Pediatrics recommends placing all infants on their backs for every sleep, including naps. Back sleeping dramatically reduced sleep-related infant deaths after it became the standard recommendation in the 1990s. Side sleeping is considered unstable because babies in that position can easily roll onto their stomachs, where the risk of suffocation increases, especially before they have the neck and upper body strength to lift their head and clear their airway.
What Actually Keeps Your Baby on Their Back
There’s no device or product that safely prevents a newborn from rolling to the side. What works is a combination of the right sleep surface and consistent repositioning.
Use a firm, flat mattress. A mattress that meets current safety standards won’t allow your baby to sink in or create pockets of soft material around their body. If the surface passes a simple test (your baby’s head doesn’t create an indentation when placed on it) it’s firm enough. Soft or plush surfaces make it easier for a baby to shift position and harder for them to breathe if they end up face down.
Keep the sleep space completely bare. No pillows, blankets, stuffed animals, bumper pads, or rolled towels. Anything soft near your baby can become a suffocation hazard if they curl into it. A fitted sheet over the mattress is all you need.
Reposition gently when you see it happen. If you place your baby on their back and they curl to the side, roll them back. You don’t need to stay awake watching for this all night. Place them on their back at the start of every sleep, and if you happen to notice they’ve shifted, move them back. As the reflex fades over the coming weeks, you’ll need to do this less and less.
Try a snug swaddle. A proper swaddle keeps your baby’s arms close to their body, which can reduce the muscle contraction that pulls them to the side. It also dampens the startle reflex, which helps them stay settled on their back. Make sure the swaddle is snug around the arms and chest but loose enough around the hips for healthy leg movement.
Do Not Use Sleep Positioners
Wedges, bolsters, and “anti-roll” pillows are marketed to keep babies in position, but they are genuinely dangerous. The U.S. Consumer Product Safety Commission and the FDA issued a joint warning after documenting 12 infant deaths over a 13-year period in which babies suffocated in or next to sleep positioners. Most of those infants rolled from a side position onto their stomachs and couldn’t free themselves.
Beyond the reported deaths, dozens of additional cases involved babies found in hazardous positions within or beside these products. The FDA has never cleared any sleep positioner for reducing the risk of SIDS or suffocation. Both agencies are clear: stop using them entirely. A bare, firm mattress is safer than any positioning product.
When to Stop Swaddling
Swaddling helps in the early weeks, but it becomes a hazard once your baby starts showing signs of intentional rolling. A swaddled baby who rolls onto their stomach has no way to use their arms to push up or turn their head for clear breathing. Watch for these signs that it’s time to transition out of the swaddle:
- Attempting to roll when unswaddled during awake time
- Pushing up on hands during tummy time and lifting one hand off the ground
- Fighting the swaddle or becoming fussy when wrapped
- Trying to free their hands up near their face while swaddled
- Loss of the startle reflex, even if rolling hasn’t started yet
Once you see any of these signs, switch to a wearable blanket or sleep sack that leaves the arms free. Your baby needs their arms available to reposition themselves and keep their airway clear if they roll during sleep.
When Rolling Becomes Normal
Most babies develop the strength to roll intentionally (tummy to back) by around 6 months, though every child hits this milestone on their own schedule. Once your baby can roll both ways consistently, you no longer need to reposition them if they shift during sleep. At that point, you still place them on their back at the start of every sleep, but if they choose to roll onto their side or stomach on their own, they can stay there.
The newborn curl that prompted your search is a short-lived phase. Within a few weeks, your baby’s flexion reflex will relax, and they’ll stay on their back more easily. Until then, a firm mattress, a bare sleep space, and consistent back-placement every time you put them down is the full solution.