Sleep is crucial to a newborn baby's health—as well as every parent's sanity, but there is more to getting a good night's rest than a simple blanket.

Newsweek asked the experts to explain how to dress a baby for sleep and whether parents should use a swaddle or a sleep sack — or both.

Swaddling is a traditional practice of wrapping a baby up gently in a light, breathable blanket.

The American Academy of Pediatrics (AAP) says that when performed correctly, "swaddling can be an effective technique to help calm infants and promote sleep."

Jenny Ward, CEO of the Lullaby Trust, describes this to Newsweek as "like a cocoon, to keep them in one place, so arms and legs can't move around."

Amy Motroni, Pediatric Sleep Consultant at The Postpartum Party, adds swaddles are "appropriate for babies to wear up until they are about 12 weeks old or until your baby starts to show signs of rolling."

She told Newsweek: "After that, your baby needs their arms free and it's time to transition them to a sleep sack to keep them warm and safe."

A sleep sack is an alternative wearable blanket, allowing parents to keep their little one warm without using loose blankets.

Jenny Ward describes the item as, "literally like a sleeping bag for a baby, so they have far more movement, their arms aren't usually in the bag at all, it's just in the shoulders, so the legs can move around within the sack."

Dr. Harvey Karp, pediatrician, child development expert and CEO of Happiest Baby Inc, believes using a newborn sleep sack "makes it way easier to swaddle your baby."

He told Newsweek: "Rather than dealing with blankets of all sizes and shapes, and worrying about using the right tucks and folds, you just place your baby in the swaddle sack, and voila!

"The good news is that babies tightly wrapped like little burritos are happy ones! When in a sleep swaddle, babies recall the familiar feeling of life in the womb, and the calming reflex turns on."

Dr. Nilong Vyas, a Board-Certified Pediatrician and Sleep Coach with Sleepless in NOLA, describes sleep sacks as being helpful after the baby is a few months old.

He told Newsweek: "Sleep sacks can be utilized once the baby is rolling and would need their arms and hands-free to assist in the rolling process.

"Sleep sacks can be used well into toddlerhood and can be something children identify with the bedtime routine and process."

Research shows a "clear link" between overheating and an increased risk of sudden unexpected death in infancy, so it is important parents and carers know how to dress baby for sleep.

Red Nose, a child death support charity, states on its site how babies control temperature predominantly through their head and face, adding: "This is why we recommend that you put baby to sleep on their back with head and face uncovered."

As a result, the not-for-profit recommends parents always ensure head coverings are removed before sleep and ensure the infant lies with feet at the bottom of the cot, and are "firmly tucked in to prevent baby from wriggling down and overheating."

The American Academy of Pediatrics (AAP) also highlights the importance of placing a baby to sleep on his back, when being put to sleep, to reduce the risk of Sudden Infant Death Syndrome (SIDS).

The AAP's Dr. Rachel Moon is quoted as saying: "This may be even more important if your baby is swaddled. Some studies have shown an increased risk of SIDS and accidental suffocation when babies are swaddled if they are placed on their stomach to sleep, or if they roll onto their stomach.

"If babies are swaddled, they should be placed only on their back and monitored so they don't accidentally roll over."

Dr. Harvey Karp adds: "Safe swaddling can actually help prevent cot death by making it more difficult for your baby to roll.

"This is important because SIDS risk jumps eight to 45 times for babies who routinely back sleep, but accidentally roll."

Babies are born with a startle (Moro) reflex, meaning should a baby's arms and legs flail suddenly, it can cause the newborn to be more awake and unsettled.

Debra Jonckers, an antenatal and postnatal teacher and Founder of Birth Matters, says swaddling "reproduces the deep pressure, neutral temperature and firm touch of being in the womb, which makes them feel calmer.

She told Newsweek: "It also enables them to keep their hands close to their mouth so they can suck on them to self-soothe."

Jonckers suggests if you are going to swaddle your baby, "you should do it from birth."

She said: "Don't introduce swaddling at two to three months, when the risk of SIDS is at its highest.

"By then, your baby will have got used to going to sleep without swaddling, so a change in her sleeping habits may make her more vulnerable." For healthy development of the hips, make sure that you give your baby plenty of room to move her legs and feet.

Baby Sleep Expert Hannah Love told Newsweek: "Some evidence suggests that if legs are firmly swaddled together in a straightened-out position there is potential for damage to normal hip development.

"By leaving the bottom loose and untucked, you can reduce this risk and allow those little legs to move freely." She also shared the following advice on how to dress your baby for sleep.

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