A newborn should sleep in a single layer of fitted clothing, like a onesie or footed pajama, plus a swaddle or wearable sleep sack, and nothing else. The sleep surface should be a firm, flat mattress inside a safety-approved crib or bassinet with only a fitted sheet. No blankets, pillows, stuffed animals, or bumper pads.
Getting this right matters more than most new parents realize. The specifics of what your baby wears and where they lie down are directly tied to reducing the risk of SIDS and sleep-related suffocation.
The Sleep Surface: Crib, Bassinet, or Play Yard
Your newborn needs a firm, flat surface for every sleep, whether it’s nighttime or a five-minute nap. That means a crib, bassinet, or play yard that meets current safety standards. The mattress should fit snugly inside the frame with no more than about three inches of gap in the corners. If you can fit more than two fingers between the mattress edge and the side of the crib, the mattress is too small.
The only thing on that mattress should be a tight fitted sheet. No blankets, no quilts, no crib bumpers, no positioners, no pillows. Crib bumpers and inclined sleepers (anything angled more than ten degrees) are now banned from sale in the United States by the Consumer Product Safety Commission. If you received one as a hand-me-down, don’t use it.
Place the crib or bassinet in your bedroom for at least the first six months. Room sharing (not bed sharing) can reduce the risk of SIDS by as much as 50%. One study found that not room sharing increased the chance of sleep-related suffocation by more than 18 times compared to sleeping in the same room as a parent.
What to Dress Your Newborn In
Start with a base layer: a short-sleeve or long-sleeve onesie, or a footed sleeper depending on room temperature. Over that, you’ll add either a swaddle (for the first couple of months) or a sleep sack. That’s the whole outfit. No hats indoors, no mittens, no extra blankets tucked around them.
The general rule is to dress your baby in one layer more than you’d be comfortable in. If you’re fine in a T-shirt, your baby likely needs a onesie plus a light sleep sack. If the room feels cool and you’d want a sweater, a footed pajama under a warmer sleep sack is appropriate.
To check whether your baby is too warm or too cold, feel the back of their neck or their chest. Hands and feet tend to run cool on newborns regardless, so they’re not a reliable indicator. If their chest feels sweaty or hot, remove a layer. Overheating is a known risk factor for SIDS.
Room Temperature and TOG Ratings
Keep the nursery between 68 and 78°F. Many parents find the sweet spot is around 68 to 72°F. A simple room thermometer near the crib takes the guesswork out.
Sleep sacks and swaddles are often rated using a TOG system, which measures thermal resistance. Higher TOG means warmer. Here’s a practical guide:
- Above 75°F: A 0.2 or 0.3 TOG sack (very lightweight, almost like a single layer of cotton) or just a onesie alone
- 69 to 75°F: A 1.0 TOG sack with a short-sleeve onesie underneath
- 63 to 69°F: A 2.5 TOG sack with a long-sleeve onesie or footed pajama
- Below 63°F: A 3.5 TOG sack with a footed pajama underneath
Not all brands use TOG ratings, but the concept still applies: thinner fabric for warmer rooms, heavier fabric for cooler ones. When in doubt, go lighter. It’s easier for a baby to warm up slightly than to cool down from overheating.
Swaddling a Newborn Safely
Most newborns sleep better when swaddled because it mimics the snug feeling of the womb and reduces the startle reflex that wakes them. You can use a traditional swaddle blanket or a zip-up swaddle product. Both work, but zip-up versions are harder to get wrong.
The key safety detail is what happens below the waist. Your baby’s legs need room to bend, spread apart, and move freely. In the womb, a baby’s legs are bent up and crossed. Forcing them straight down and pressed together during swaddling can damage the soft cartilage of the hip socket and increase the risk of hip dysplasia. The International Hip Dysplasia Institute recommends that swaddled babies’ hips stay in slight flexion (bent) with the knees apart. Think of a frog-leg position. The swaddle should be snug around the arms and chest but loose and open around the hips and legs like a pouch.
If you’re using a blanket swaddle, fold or twist the bottom of the fabric and tuck it loosely behind the baby so the legs can move naturally. If you’re buying a commercial swaddle, look for one with a wide, open sack at the bottom rather than a tight, tapered shape.
When to Stop Swaddling
You must stop swaddling the moment your baby shows any signs of rolling over, even if it’s only a partial roll. A swaddled baby who ends up face-down cannot push up or reposition, which creates a suffocation risk. This transition happens at different ages for different babies but typically falls between 2 and 6 months, sometimes earlier.
Watch for these signs: pushing up during tummy time, rolling from back to side, or arching the back and rocking. If you see any of these, it’s time to switch from a swaddle to a sleep sack with arms free. Some transitional products have removable arm wings that let you free one arm at a time over a few nights, which can ease the change.
Products to Avoid
Weighted swaddles and weighted sleep sacks are not safe for infants. The American Academy of Pediatrics published recommendations in 2022 stating that weighted products should not be placed on or near a sleeping infant. Testing has shown these products are associated with drops in oxygen levels, which can be harmful to a developing baby’s brain. Several major retailers have pulled weighted infant sleep products from their shelves.
Other items that should never be in or on the sleep space:
- Inclined sleepers and rockers used for sleep: Banned by the CPSC due to infant deaths
- Crib bumpers: Also banned, including padded bumpers and vinyl bumper guards (non-padded mesh liners are not included in the ban, but most pediatric organizations still recommend a bare crib)
- Loose blankets or quilts: Use a wearable sleep sack instead
- Pillows, stuffed animals, or soft bedding: Soft surfaces significantly increase the risk of suffocation
- Positioning wedges or nests: These can create pockets of rebreathed air around a baby’s face
Always on Their Back
Place your baby on their back for every sleep, every time. Back sleeping dramatically reduces the risk of SIDS compared to side or stomach sleeping. Once your baby can roll both ways on their own (usually around 4 to 6 months), you don’t need to reposition them if they roll during sleep, but always start them on their back. By that age, they should be out of the swaddle and in a sleep sack with free arms, so they can adjust their own position if needed.