Exploring Theories on the Cause of Sudden Infant Death Syndrome (SIDS)

What Is SIDS?

According to the Mayo Clinic, sudden infant death syndrome (SIDS) is the death of a child under one who does not have any health issues and cannot be explained. SIDS may also be referred to as sudden unexpected infant death or SUID. SIDS deaths are common during sleep, so the condition may colloquially be called crib death.

Estimates from the CDC note that roughly 3,400 sudden unexpected infant deaths occur in the United States each year. While unknown causes and accidental suffocations or strangulations are associated with sudden unexpected infant death, the CDC notes that SIDS is the leading cause of SUID, accounting for 1,389 cases in 2020.

In 1990 the rate of SIDS was 130.27 deaths per 100,000 live births. Since then, the rate of SIDS has decreased significantly, accounting for 38.4 deaths per 100,000 live births in 2020.

While the actual cause of SIDS is unknown, many researchers and clinicians believe it may be associated with a brain abnormality that leaves a child unable to control breathing or prevents the child from waking up when they cannot breathe during sleep.

SIDS Risk Factors

Even without a confirmed cause of SIDS, healthcare providers have been able to narrow down risk factors that may increase the risk of SIDS. The Mayo Clinic divides these risk factors into physical, sleep environment, maternal, and other factors.

Physical

Brain defects are among the physical risk factors associated with an increased risk of SIDS. Coinciding with the theory that brain abnormalities cause SIDS, researchers have noticed that a brain defect is linked to higher rates of SIDS.

Beyond brain defects, other physical risk factors such as low birth weight or respiratory infection may contribute to higher rates of SIDS. Premature or multiple births are often associated with low birth weight, increasing the probability that the infant’s brain did not develop fully before delivery. As a result, a baby may not be able to regulate breathing or heart rate as well as those born with an average weight.

A history of respiratory illness may also damage the lungs and contribute to breathing problems. According to the Mayo Clinic, there are high rates of SIDS in infants who have had a cold recently.

Sleep Environment

In addition to the physical risk factors associated with SIDS, there are also factors in an infant’s sleep environment that could put them at a higher risk of SIDS. For example, being put to sleep on their stomach or side can make breathing difficult for an infant. Bed-sharing and sleeping on a soft surface may also be associated with a higher risk of SIDS. Finally, overheating while sleeping may cause sudden infant death.

Maternal

Maternal risk factors may also significantly increase SIDS risk. According to the Mayo Clinic, being under 20, smoking cigarettes, using drugs or alcohol, and having inadequate prenatal care are maternal risk factors for SIDS.

Other

Aside from maternal, physical, and environmental sleep factors, other traits are associated with SIDS. Many sources state that SIDS risk is higher in boys. Additionally, the risk is highest between two and four months old. Some resources say that a family history of SIDS may increase the probability of sudden infant death. Additionally, environmental factors that affect breathing, such as second-hand smoke, may escalate SIDS risk.

Additionally, many resources note that SIDS is more common in non-White infants. The CDC states, “Although the SUID rate has declined since the 1990s, significant racial and ethnic differences continue.”

Data from the CDC notes that non-Hispanic Native Hawaiian or Other Pacific Islander infants have the highest rates of SIDS at 87.2 deaths per 100,000 live births, more than double the national average. The rates of SIDS among non-Hispanic American Indian/Alaskan Natives and non-Hispanic Black individuals are similar at 73.1 and 73.9 deaths per 100,000 live births, respectively. These rates are still nearly double the national average.

Non-Hispanic White infants have a SIDS rate of 34.8, just under the US average. Finally, Hispanic and non-Hispanic Asian infants have the lowest SIDS risk at 20.2 and 7.7 deaths per 100,000 live births, respectively.

While few sources fully explain why that is the case, many believe that racial inequity and limited healthcare accessibility among marginalized communities contribute to inadequate care and parental education, which can be linked to higher SIDS rates.

SIDS Prevention Strategies

While there is no foolproof way to prevent SIDS, researchers and clinicians have some guidelines that minimize the risk of sudden infant death. Chief of these suggestions is practicing safe sleep habits. Although different resources present safe-sleep habits in different ways, generally, they have some things in common.

Some safe sleep strategies include laying an infant on their back to sleep, keeping a crib bare, monitoring an infant’s temperature to prevent them from overheating, keeping the baby’s crib in the parent’s room for six months to one year, and avoiding bed-sharing.

An ongoing study by Johns Hopkins University is analyzing the use of an infant sleep assessment (ISA) tool and motivational interviewing (MI) for the provider–parent communication on safe sleep during a baby’s well visit. While the study is still recruiting participants, researchers hypothesize it will improve effective communication on sleep practices, reducing SIDS risk.

Additional strategies that have been linked to lower rates of SIDS include the following:

• breastfeeding for a minimum of six months if possible
• offering a pacifier to a baby at naptime or bedtime, being sure to avoid pacifiers with strings and after scheduling a nursing routine if breastfeeding
• getting routine immunizations as the CDC and American Academy of Pediatrics advise

Despite common misconceptions, the American Academy of Pediatrics warns against relying on baby monitors and other devices that are promoted for reducing SIDS. The Mayo Clinic notes that these devices have not been adequately tested for SIDS and may be ineffective or cause safety issues.

SIDS Diagnosis and Next Steps

A SIDS diagnosis is concluded post-mortem when an autopsy, review of clinical history, and death-scene investigation do not provide an explanation or reason for death. Boston Children’s Hospital refers to this as a diagnosis of exclusion.

A Sudden Unexpected Infant Death Investigation Reporting Form (SUIDIRF) may be completed after cases of SUID. While voluntary, the form can help the CDC, individual states, and other jurisdictions gather information on SUIDs and improve research efforts. The tool was developed in 1996 but has been updated multiple times, with the most recent version released in 2020.

According to the CDC, the form collects information on pregnancy history, infant demographics, and history, incident scene investigation and circumstances, a summary and diagrams of the investigation, and a summary for the pathologist.

SIDS Theories

Boston Children’s Hospital notes that there are some theories about SIDS, despite no conclusive causes.

Triple-Risk Model

One theory the organization highlights is the triple risk model, which postulates that SIDS only occurs when an infant is in a vulnerable stage, exposed to a triggering event, and has an underlying issue preventing them from appropriately responding to low oxygen levels.

Biomarker Theory

More recently, a study published in eBioMedicine identified a potential biomarker for SIDS. Researchers used dried blood spots collected during newborn metabolic screenings to measure butyrylcholinesterase (BChE) levels. According to the study, BChE is “an enzyme of the cholinergic system, a major branch of the autonomic system, and may provide a measure of autonomic (dys)function.”

The study concluded that babies who died of SIDS had lower levels of BChE, indicating that reduced BChE activity was a risk factor for SIDS. Although the study yielded exciting results, additional research is needed to confirm these findings.