What Is Sudden Infant Death Syndrome (SIDS)?

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Sudden infant death syndrome (SIDS) refers to the unexpected, unexplained death of an infant less than a year old. For a diagnosis of SIDS, the cause of death remains unclear even after a complete investigation. This may include an autopsy, taking a complete medical history, and reviewing the scene of death.

Sudden Infant Death Syndrome SIDS definition

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Causes

Most SIDS deaths are associated with sleep, and some people still refer to SIDS as “crib death.”

The exact cause of SIDS remains unknown, but researchers have a number of theories.

A growing body of research suggests that infants who die from SIDS have brain abnormalities or defects since birth. These defects are often found in the part of the brain that controls:

  • Breathing
  • Blood pressure
  • Heart rate
  • Waking from sleep

Researchers believe that in addition to brain defects, other events must occur for an infant to die from SIDS. Scientists describe this using a triple risk model.

Under this model, three factors all have to occur at once for an infant to die from SIDS. Having only one factor occur may not result in death from SIDS, but if all three occur, the chance of death from SIDS is higher.

The three factors include:

  • An at-risk infant: This includes an infant that may have an unknown problem like a brain defect or genetic change.
  • Time in infant’s development: In the first six months of life, infants experience multiple quick phases of growth which change how well the body regulates itself.
  • Environmental stressors: Examples include being overheated, being placed on the stomach to sleep, and being exposed to cigarette smoke.

Infants who don’t have either of the first two factors may be able to overcome any environmental stressors and survive, but infants who may have an unknown problem, together with body systems undergoing a change, may not be able to handle such stressors.

All three factors need to occur for SIDS to be considered the cause of death.

Risk Factors

No single factor means a baby is at greater risk of SIDS. Rather, a combination of factors may cause an infant to die of SIDS. Data about SIDS include:

  • The majority of SIDS deaths occur in babies aged between two to four months.
  • More boys than girls die from SIDS.
  • Black and Native American infants are more likely to die due to SIDS than Caucasian infants.

There are a number of other possible risk factors for SIDS, including:

  • Use of drugs, drinking, or smoking during pregnancy
  • Prematurity or a low birth weight
  • Poor prenatal care
  • A family history of SIDS
  • A mother younger than 20 years old
  • Infant exposure to tobacco smoke
  • Overheating

Eliminating External Risk Factors

Eliminating external risk factors, like environmental stressors, is the most effective way to reduce the risk of SIDS.

How to Prevent SIDS

Creating a safe sleeping environment is important to prevent SIDS. Here are some tips to avoid SIDS in babies up to one year old.

Babies Should Sleep on Their Backs

Infants who sleep on their back are at less risk of SIDS than babies who sleep on their stomach or on their side. Some babies roll onto their stomach on their own.

What if My Baby Rolls Onto Their Stomach on Their Own?

If your baby can roll from back to stomach and stomach to back, you do not need to move your baby onto their back. Make sure there are no items surrounding the baby that they could roll into and block airflow.

If your baby falls asleep in the car, a baby carrier, or a stroller, move your baby to a sleep surface on their back as soon as you can.

A Firm Sleep Surface Should Be Used

Cribs, bassinets, and portable cribs must meet the safety standards set out by the Consumer Product Safety Commission. A firm mattress that is tight-fitting, as well as a fitted sheet designed for the specific product, is recommended.

A firm surface is considered one that should be hard and not indent when a baby is lying on it. Nothing else but the baby should be in the crib.

Do Not Share a Bed With Your Baby

The American Academy of Pediatrics (AAP) does not recommend bed sharing for any baby.

You should only bring your baby into your own bed to feed or comfort them. The baby should be placed on their back in their own bed when you are ready for sleep.

If there is a chance you will fall asleep with the baby in your bed, ensure there are no pillows, blankets, or other things that could cover the baby’s head or overheat your baby.

Share a Room With Your Baby

For at least the first six months, and ideally for the first year, the AAP recommends the baby sleeps in the same room as the parents. The crib or bassinet should be placed close to your bed. This can decrease the risk of SIDS by up to 50%.

Keep Objects Out of the Baby’s Crib

Loose bedding, soft objects, or any item that could increase the risk of suffocation, strangulation, or entrapment should be kept away from where the baby sleeps. This includes:

  • Blankets
  • Toys
  • Bumper pads

If you’re concerned your baby will be cold, you can dress them in sleep clothing.

Do Not Let Your Baby Fall Asleep on Nursing Pillows, Couches, or Armchairs

The Consumer Product Safety Commission states that more than two dozen infants died between 2012 and 2018 from being left on or near nursing pillows or pillow-like lounging pads.

Babies should never be left to sleep on couches, sofas, or armchairs. This is dangerous for the baby.

Use Pacifiers at Naps and Bed Time

Using a pacifier during naps and bedtime can help reduce the chance of SIDS, even if it falls out when the baby is sleeping.

If breastfeeding, wait until breastfeeding is going smoothly before trying a pacifier. Those not breastfeeding can offer a pacifier straight away. If a pacifier falls out during sleep, you don’t have to replace it.

Coping

If you have experienced the loss of an infant, it is important to seek support. Support groups include:

A Word From Verywell

It can be distressing to read about SIDS, but there are steps you can take to ensure your baby is safe and to reduce their risk. If you have any concerns about your baby’s health, or questions about appropriate and safe sleeping arrangements, speak with your healthcare provider.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institutes of Health. About SIDS. Updated January 31, 2017.

  2. Johns Hopkins Medicine. Sudden infant death syndrome (SIDS).

  3. National Institutes of Health. What causes SIDS? Updated January 31, 2017.

  4. American Academy of Pediatrics. How to keep your sleeping baby safe: AAP policy explained. Updated December 23, 2020.