Sudden infant death syndrome (SIDS) is the unexpected, sudden death of an infant under the age of 1 with no known cause. Most SIDS deaths occur when an infant is between the age of 1–4 months.
SIDS is the unexplained and unexpected death of a seemingly healthy infant under the age of 1 year old. SIDS generally occurs when an infant is sleeping.
The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) states that SIDS is the leading cause of death for infants between 1 and 12 months old. They also note that SIDS causes around half of sudden infant deaths in the United States each year.
Although SIDS can occur at any age below 1 year old, it is more common during certain ages than others. This article will go into detail about the risk of SIDS at different ages, as well as risk factors and prevention.
Share on PinterestDesign by Diego Sabogal
SIDS can occur until an infant is a year old. After that, unexplained death is called sudden and unexplained death in childhood (SUDC).
SIDS is more likely to occur at certain ages than at others.
The NICHD notes that SIDS is most common when an infant is between 1–4 months old. Additionally, more than 90% of SIDS deaths occur before the age of 6 months old.
The risk of SIDS reduces after an infant is 8 months old. However, parents and caregivers should maintain safe sleep practices until a child is over a year old.
The cause of SIDS is currently unknown. This makes it difficult for researchers to understand why SIDS is more common at certain ages than others.
Research from 2018 mentions that one theory for SIDS is nervous system “abnormalities.” Changes in the neural control of an infant occur at around 2–4 months, a period when SIDS is most likely to occur.
However, this is currently only a theory, and there is little evidence to confirm it as a cause for SIDS.
Researchers consider SIDS to be the result of many factors, rather than just one. When these factors overlap, an infant may have a higher risk of SIDS.
Possible risk factors for SIDS include:
- being a male infant
- being born prematurely
- having a low birth weight
- having possible unidentified gene mutations
- having prenatal exposure to drugs, cigarettes, or alcohol
Certain medical conditions may also increase the risk of SIDS. However, it is inconclusive how important a medical condition is in the development of SIDS.
Researchers theorize that the development of SIDS can occur due to medical conditions that affect the following:
- respiration function, such as respiratory failure
- cardiovascular function, which relates to the heart and blood vessels
- gastrointestinal function, which relates to the digestive system
- nervous system
- immune system responses
- endocrine function, which relates to hormones
- metabolism
- biochemistry, which relates to chemical processes in the body
Inadequate nutrition and a buildup of toxins have also been put forward as possible risks for SIDS. However, there is no conclusive evidence that any of these factors cause SIDS.
Other risk factors for SIDS include:
Sleep-related factors
SIDS usually occurs when an infant is sleeping. Researchers consider sleeping position to be a risk factor in the development of SIDS. SIDS is more likely to occur when an infant is asleep on their side or stomach.
A person should place a child on their back when putting them to sleep.
The NICHD also notes that bedding can also be a factor in SIDS. Having blankets, toys, crib bumpers, or other soft objects in an infant’s crib can increase their SIDS risk. Loose objects in a crib have the potential to cause suffocation or entrapment.
Lying an infant on a soft surface, such as a couch or mattress, can increase their SIDS risk. This is because the surface compresses under the infant, causing them to become trapped if they roll onto their stomach.
Altered sleeping patterns may also have an effect on SIDS risk. Altered sleep states may affect an infant’s ability to respond to stressors, which may lead to increased vulnerability during sleep.
Sleeping with another person can also be a factor in SIDS development. If a person falls asleep on a bed or sofa beside an infant, there is a possibility they may roll onto them, causing suffocation. This is also a possibility if a person falls asleep while holding or nursing an infant.
Geographical location and climate
The risk of SIDS can be higher in certain parts of the world.
This could be due to colder climates in certain areas. SIDS is more common during colder months than during the summer. This may be due to a person over-bundling their infant in blankets or clothes, leading to overheating.
Ethnicity
SIDS rates can vary depending on an infant’s ethnicity.
Research from 2018 found that SIDS rates were lower in infants with an Asian heritage. Alternately, SIDS rates were higher in infants with an African American heritage or a Native American or Alaska Native heritage.
These variances may be due to geographical location, socioeconomic factors, or differences in child care practices.
It is important to note that there is a disparity in the amount of research relating to health conditions in Communities of Color.
There may be other reasons that SIDS appears to occur more often in certain populations, such as not having the same access to healthcare and mistrust of healthcare professionals due to systemic racism.
Parental characteristics
SIDS is more likely if an infant’s birth parent has:
- maternal anemia
- inadequate prenatal care
- inadequate prenatal nutrition
- multiple births less than 1 year apart
- used drugs or alcohol during pregnancy
Being a single parent and giving birth to a child at a young age appear to have an association with higher occurrences of SIDS.
There are various ways a person can help reduce the risk of SIDS, such as by:
- always lying their infant on their back to sleep
- keeping soft objects, such as toys and blankets, out of an infant’s crib
- using a firm, flat sleep surface for the infant
- breastfeeding or chestfeeding
- sharing a room with the infant until they are 1 year old, keeping them close but on a separate surface
- having regular prenatal checks
- using a pacifier during sleep once nursing is established
- preventing the infant from overheating during sleep
- following healthcare guidance on vaccines and checkups
- allowing the infant to spend time on their stomach, or tummy time, when they are awake and being watched
Parents and caregivers should avoid:
- products such as wedges or positioners in the infant’s crib
- smoking or drinking during pregnancy
- car seats, strollers, swings, or carriers as the infant’s regular sleep spot
Learn moreIt is important that an infant has a safe sleeping environment. Learn more about infants and safe sleeping:
SIDS has no warning signs, and infants generally seem healthy beforehand.
A person should contact a doctor if they have any worries or concerns about their infant. Healthcare professionals can discuss the best ways for a person to prevent SIDS from occurring.
If a person notices that their infant is unresponsive or having trouble breathing, they should seek immediate medical attention.
SIDS is the unknown and unexpected death of an infant before they are 1 year old. SIDS has no warning symptoms and can occur in seemingly healthy babies.
Although SIDS can occur at any age before 12 months, it is most common when an infant is between 1–4 months old. SIDS is less common after an infant is 8 months old, but a person should still take precautions to reduce the risk.
Researchers believe SIDS may be the result of several overlapping factors. However, there is no definitive cause.
There are many ways a person can reduce an infant’s risk of SIDS. One of the most important preventive measures is to always lay an infant to sleep on their back.
If a person is concerned about their infant, they should speak to a healthcare professional.
Sudden Infant Death Syndrome (SIDS), the unexplained sudden death of an infant under the age of one year, affects approximately 1500 infants annually. Its exact cause remains a mystery, but a recent study in Pediatrics has revealed a possible risk factor. Researchers have found that an infant who is swaddled – wrapped tightly in a blanket or cloth with their limbs restricted – while placed on their front or stomach to sleep faces a higher risk of SIDS.
Thomas Keens, MD, faculty member in the division of Pediatric Pulmonology and Sleep Medicine and director of the Cystic Fibrosis Care Center at Children’s Hospital Los Angeles, spoke to us about the implications of this study. Keens is also Chair of the California SIDS Advisory Committee, which advises the California Department of Public Health on issues related to SIDS.
Is there a hypothesized cause for SIDS?
The cause of SIDS remains unknown. However, most SIDS researchers believe in the triple risk hypothesis of SIDS. That is, SIDS is not due to one abnormality in one physiological system. Rather, researchers now believe it is due to an interaction of three factors. First is the developmental window of vulnerability. SIDS is most common at 2-4 months of age when the cardiorespiratory system of all infants is in rapid transition and therefore unstable. So, all infants in this age range are at risk for dysfunction of neurological control of breathing.
The second factor is environmental challenges, which vary from sleeping in a prone (on the stomach) position and soft bedding to overheating and second hand tobacco exposure. Third, some infants are intrinsically vulnerable and have differing abilities to respond to different stresses.
This hypothesis is supported by recent research out of Harvard University, which has shown the brainstem levels of serotonin – a neurotransmitter important in life support functions in the brain like breathing and heart rate – is decreased in children who died of SIDS. This suggests that in this triple risk hypothesis, those infants who die have increased vulnerability (decreased life support neurotransmitters). In another scenario, not all babies sleeping prone in soft bedding would die, but those who die were probably less able to deal with the environmental challenge of the prone position and soft bedding.
This remains a hypothesis, but most SIDS researchers believe this combination of multiple factors is the mechanism of death in these babies.
How could swaddling be potentially increasing risk of SIDS?
Prone sleeping is the single most important risk factor for SIDS. If a baby is swaddled, and placed prone to sleep, that infant has no ability to try to lift or turn his/her head to avoid a potentially dangerous situation where the face is buried in bedding. Even if babies are placed on their backs to sleep, they begin to roll over at ~3-4 months of age, some earlier. If a swaddled infant rolls from the back to the stomach, he/she cannot move to try and correct the position. Therefore, the infant will be in the most dangerous position. Suffocation is possible. If an infant is swaddled with thick blankets, this can lead to overheating, which is another high risk factor for SIDS. If the infant is swaddled with blankets covering the face, this is yet another risk factor for SIDS.
Thus, if infants are swaddled, which is often done to encourage sleep, they should always be placed supine and be swaddled in thin blankets to prevent overheating. The face should not be covered, and swaddling should be discontinued when the infant may begin to roll from supine (on the back) to prone, which is at about 3-months. Increasingly, the recommendation by physicians is to stop swaddling when the infant is 2-months of age.
What are some other risk factors for SIDS?
Other risk factors for SIDS (which have been shown to increase risk for but not necessarily cause SIDS) include unsafe bedding (a soft mattress as opposed to a firmer one), having items in the crib with the infant, cigarette smoke exposure, bedsharing (i.e. infants sleeping in the parents’ bed), and overheating.
What SIDS-related research has been conducted here at CHLA?
CHLA has a proud legacy of contributing to SIDS research. As late as the late 1980’s, many believed that SIDS was due to babies not breathing during sleep (apnea). We were one of the first to show that recordings of breathing and heart rate did not predict SIDS or serious apneic events in high risk infants.
So, we focused our attention on a different question. Because infants have an immature respiratory control, all infants have many breathing pauses. We reasoned that is may not be so important to know why they have apneas, but to understand if and how they can rescue themselves from these pauses. If an infant has a prolonged breathing pause, he/she could become hypoxic (low oxygen). So, can these infants rescue themselves from a breathing pause by waking up in response to the low oxygen? We found that even normal infants seem to be born with an ability to awaken in response to low oxygen, but they lose this at ~2-3 months of age, which is when the incidence of SIDS peaks. We do not think this is the cause of SIDS, but we think it is one of the factors which makes every infant more vulnerable to SIDS at the peak age of 2-4 months. We also were the first to describe an increased SIDS risk for infants of substance abusing mothers.
CHLA continues to promote SIDS risk reduction and safe infant sleep education, including promoting a safe infant sleep environment in CHLA. We have been active in the education of county public health nurses to support families who have experienced the devastating death of an infant from SIDS.
Any additional comments?
My interpretation of this study is that it is not perfect. There are relatively small numbers of SIDS and controls, but the data obtained differed between studies. I agree with the authors that this study is not powerful enough to prove that swaddling increases the risk for SIDS. However, it does reinforce two current recommendations: (1) Swaddled infants should never be placed prone (on the stomach); and (2) if started, swaddling should be stopped at 2-3 months of age when an infant begins to roll over because the danger of a swaddled infant on the stomach who cannot move.
Image courtesy of Shutterstock.