Place your newborn on their back, on a firm and flat mattress, with nothing else in the crib. That single practice is the foundation of safe infant sleep. After the back-to-sleep recommendation became widespread in the 1990s, sleep-related infant deaths dropped significantly, and back sleeping remains the most important thing you can do every time you lay your baby down.
The Back-to-Sleep Position
Every sleep, whether a nap or nighttime, your baby should go down on their back. Babies who sleep on their backs are far less likely to die of SIDS than babies placed on their sides or stomachs. This applies even if your baby seems to prefer turning their head to one side or fusses initially. Once babies can roll both ways on their own, you don’t need to reposition them, but always start on the back.
How to Lower Your Baby Without Waking Them
The moment you lift a sleeping baby away from your chest and lower them toward a flat surface, the sudden feeling of falling can trigger the startle (Moro) reflex, and you’re back to square one. Two techniques help avoid this.
The first is to lower your baby so their side touches the mattress first, then gently roll them onto their back. The second is to let their bottom and legs make contact first, then slowly lower the upper body and head. Both approaches keep your baby’s body partially supported throughout the transfer instead of creating the free-fall sensation that triggers a startle. Keep your hands on them for a few seconds after they’re fully down before slowly sliding them away.
What Goes in the Crib (and What Doesn’t)
The only things that belong in your newborn’s crib are a firm, flat mattress and a single fitted sheet made specifically for that crib. That’s it.
Remove pillows, quilts, comforters, sheepskins, stuffed animals, and bumper pads, including the thinner “breathable” mesh ones. Loose blankets are a suffocation risk. If you’re worried about your baby being cold, dress them in a wearable blanket (sleep sack) instead. The CDC specifically notes that weighted versions of sleep sacks, swaddles, and blankets are not safe for infants.
Getting the Mattress Right
A newborn’s mattress needs to be firm enough that it doesn’t conform to the shape of their face if they turn their head. Federal safety standards now require crib mattresses to pass a firmness test: a weighted tool is placed on the surface, and if the mattress gives enough to make contact with a sensor bar set just 15 millimeters above it, the mattress fails. In practical terms, press your hand into the mattress. It should spring back immediately and not leave an impression. If it feels soft or cushiony, it’s not safe for infant sleep.
The mattress should also fit snugly in the crib frame. If you can fit more than two fingers between the mattress edge and the crib side, the mattress is too small and creates an entrapment risk.
Swaddling in the Crib
Swaddling can help calm a newborn and reduce the startle reflex that wakes them during transfers. To swaddle safely, keep the blanket snug but positioned below your baby’s chin, aligned with the shoulders. Use no more than two thin swaddling blankets to prevent overheating, and make sure the wrap can’t come loose and cover the face.
The key deadline: stop swaddling as soon as your baby shows signs of rolling over. A swaddled baby who rolls to their stomach can’t use their arms to push up or reposition, which creates a serious suffocation risk. Many parents switch to a sleep sack at that point, which keeps arms free while still providing warmth.
Room Temperature and Overheating
Overheating is an independent risk factor for SIDS. Keep the room where your baby sleeps between 62 and 68°F (16 to 20°C). A simple room thermometer near the crib helps you monitor this. A good check: touch your baby’s chest or the back of their neck. If the skin feels hot or sweaty, they’re overdressed. Cool hands and feet alone aren’t a reliable sign that your baby is too cold.
Keep the Crib in Your Room
Room sharing, where your baby sleeps in their own crib or bassinet but in the same room as you, can reduce SIDS risk by as much as 50%. The AAP recommends this arrangement for at least the first six months. Room sharing is not the same as bed sharing. Sharing your bed, or falling asleep with your baby on a couch or armchair, significantly increases the risk of suffocation and overlay injuries.
Avoiding Inclined Surfaces
Anything that positions your baby at an angle greater than 10 degrees is not safe for sleep. That includes swings, rockers, bouncers, and car seats (when not in a moving vehicle). In a semi-reclined position, a newborn’s head can tip forward and compress their airway. If your baby falls asleep in a swing or car seat, move them to a flat crib or bassinet as soon as you can.
Preventing a Flat Spot on the Head
Because newborns spend so much time on their backs, a flat area can develop on the skull, a condition called positional plagiocephaly. It’s more common in firstborns, babies with a preferred head-turning direction, and less active infants. Back sleeping is still non-negotiable for safety, but a few strategies help protect head shape.
Alternate which direction your baby’s head faces each time you lay them down. If they tend to always look right, try positioning them so that interesting stimuli (your voice, a window) are on the left. During awake, supervised time, give your baby plenty of tummy time. This builds neck strength, encourages head rotation, and takes pressure off the back of the skull. Starting tummy time in short sessions from the first days home makes a difference. If you notice a persistent flat spot or your baby strongly resists turning their head one way, bring it up at your next pediatric visit. Early repositioning strategies are the most effective.