Research On Other SIDS Risk Factors

Studies have found that sleeping on soft surfaces, such as couches and soft mattresses, is a significant risk factor for SIDS.¹For example, in 2003, an NICHD-supported study showed that placing an infant to sleep on soft bedding posed five times the risk of SIDS as sleeping on firm bedding, such as on a safety-approved crib mattress. More striking, though, was the fact that infants who slept on their stomachs on soft bedding were at 21 times greater risk for SIDS than were infants who slept on their backs on firm bedding.²

In addition, soft and loose bedding can increase the potential risk of suffocation.³The Consumer Product Safety Commission has reported that the majority of sleep-related infant deaths in its database are related to suffocation involving pillows, quilts, and extra bedding.⁴

Researchers do not know why sleeping on such surfaces increases the risk of SIDS, but they warn that the research findings suggest the practice is highly dangerous.⁵The U.S. Consumer Product Safety Commission and the AAP jointly recommend that babies sleep on their backs on a safety-approved* mattress, free of loose bedding, including pillow-like stuffed toys and bumper pads.⁶

* Visit the U.S. Consumer Product Safety Commission website for more information about crib safety: http://www.cpsc.gov/en/Safety-Education/Safety-Guides/Kids-and-Babies/Cribs/.

Babies should be kept warm during sleep, but not too warm. Studies show that an overheated baby is more likely to go into a deep sleep from which it is difficult to arouse.^7,8,9,10,11Some evidence indicates that increased SIDS risk is associated with excessive clothing or blankets and a higher temperature in the room.

SIDS risk is higher for infants who sleep on a soft surface or with their heads covered than for infants who sleep on a firm surface or without their heads covered. It is not known whether the risk associated with head covering is related to overheating, lack of oxygen, or re-breathing exhaled air. We do know that it is a particular concern, it can be quite dangerous for some infants, and it may contribute to SIDS.¹²

Increased SIDS risk also has been associated with the season of the year. In the past, SIDS deaths have been more common during cold weather—possibly because infants are more likely to be overdressed or placed under heavier blankets, which may cause them to overheat—but statistics indicate that this association seems to be waning.¹³Studies also have found that overheating may increase the risk of SIDS for a baby who has a cold or infection.

Parents and caregivers should not overdress babies and should keep the thermostat at a comfortable temperature. In general, if the room temperature is comfortable for an adult, then it is appropriate for a baby.¹⁴

Infants whose mothers smoke during or after pregnancy are at greater risk of SIDS.¹⁵Infants born to mothers who smoked during pregnancy are three times more likely to die of SIDS than those born to mothers who did not smoke during pregnancy. Exposure to passive smoke (sometimes called secondhand smoke) in the household also doubles a baby's risk of SIDS.^16,17

Exactly how smoking during pregnancy affects the infant is not clear, but smoking might negatively affect development of the nervous system. Studies of the mechanisms underlying the association between smoking and SIDS have found that, during the last half of pregnancy, changes occur in nicotine-binding sites on the baby's brain stem, specifically in areas involved with arousal, heart and breathing functions, sleep, and body movement control.¹⁸

Infants who died from SIDS have a higher nicotine concentration in their lung tissue compared with infants who did not die from SIDS.¹⁹ This finding supports the statement that tobacco smoke exposure in the postnatal environment is important in SIDS risk^20,21. However, the mechanism for the association between secondhand smoke and SIDS is unknown.

Bed sharing among infants and family members, particularly among adults and infants, is common in some cultures in the United States.²² Many mothers share a bed with their infant because it makes breastfeeding easier and enhances bonding. Even though some believe that bed sharing might reduce the risk of SIDS because the parent is nearby to monitor the baby, studies do not support bed sharing as protective strategy for SIDS.²³

On the contrary, evidence is growing that bed sharing increases the risk for SIDS and can also lead to suffocation, entrapment or injury.²⁴In some situations, bed sharing can compound the risk posed by other factors. For example, the risk for SIDS is even higher than either risk factor alone when bed sharing occurs with:

• A mother who smokes, has recently consumed alcohol, or is fatigued
• The infant is covered by a blanket or quilt
• There are multiple bed-sharers^25,26,27,28

Research has shown that the presence of other children in the bed increases the risk of SIDS more than fivefold.²⁹In addition, bed sharing in an adult bed not designed for an infant exposes the infant to additional risks for accidental injury and death, such as suffocation, asphyxia, entrapment, falls, and strangulation. Infants younger than 4 months of age and those born prematurely or with low birth weight are at highest risk. This may be because their lack of motor skills and muscle strength make it difficult to readjust and avoid potential threats.³⁰

Bed sharing with infants—even when mothers do not smoke—is also a risk factor for SIDS.^31,32,33

The safest alternative to bed sharing may be room sharing, a situation in which the infant shares a room with the parents, but has his or her own crib, bassinet, or sleep space.^34,35The AAP recommends keeping the baby's sleep area close to, but separate from, where others sleep. Parents who wish to room share can place the infant's crib near the mother for easy breastfeeding and should return the infant to his or her own sleep area after breastfeeding. Families also should follow all other recommendations to reduce the risk SIDS and sleep-related causes of infant death.

NICHD-supported research found that infants who are accustomed to sleeping on their backs but who are then placed to sleep on their stomachs or sides are at an increased risk of SIDS—greater than the increased SIDS risk experienced by infants who are always placed on their stomachs or sides.³⁶

A 1999 study found that if infants who were usually placed to sleep on their back were then placed to sleep on their stomach or side, their risk of SIDS was seven to eight times greater than that of infants always placed to sleep on their stomach or side.³⁷

Make sure that babies always sleep on their backs. Every sleep time counts.

Parents, caregivers, grandparents, babysitters, siblings—everyone in charge of putting baby to sleep should place the baby on his or her back to sleep for every sleep time.