When is it Safe For Babies to Sleep on Their Tummy?

When is it safe for infants to tummy sleep

When is it Safe for Babies to Sleep on Their Tummy?

How many times have you walked in and found your baby sleeping on their tummy?  There is an immediate panic feeling that comes over you when you find your infant has rolled in the middle of the night and is now sleeping on his tummy.  Your heart skips a beat, and you find yourself holding your breath, as you run towards them; the panic feeling is even worse when you find them face down.  So, when is it safe for your baby to sleep on their tummy so you can relax?

We have all heard the safe sleep messages warning against placing babies to sleep on their tummy.  There is plenty of research that supports placing an infant to sleep on their back to reduce the risk of Sudden Unexplained Infant Death (SUID) and Sudden Infant Death Syndrome (SIDS). 

What isn’t clear, is when is it safe for your baby to sleep on their tummy? 

Unfortunately, parents are given false assurances from many sources, including pediatricians, that once their infant is strong enough to roll over, it is safe for their baby to sleep on their tummy. 

In this post, I will help you navigate fact from fiction in order to determine when it’s safe for your baby to sleep on their tummy.  I will use research-based evidence and compelling insight into the following topics:

Why Back Sleeping is Best

 We all know back sleeping is safest, but what many do not know is why.  According to the AAP Safe Sleep Task Force, “Asphyxia has long been thought to be the primary cause of death in many instances of SIDS, based both on the practices (eg, supine positioning and/or lack of soft bedding) known to be protective against SIDS and on the frequent autopsy finding of pulmonary edema, which is often seen with asphyxiation. Infants resting in the prone position or lying with soft bedding may rebreathe exhaled carbon dioxide, potentially leading to hypercarbia and hypoxia. If infants’ environment does not change or infants are unable to extract themselves from the hazardous situation, they will ultimately die of asphyxia.” (JAMA Pediatrics February 2017 Volume 171, Number 2)

Asphyxia occurs when the human body is deprived of oxygen.  If an infant begins rebreathing their exhaled air, carbon dioxide, they slowly deprive themselves of oxygen.  Continually rebreathing carbon dioxide, exhaled air, eventually suppresses the infant’s need to breathe which leads to hypercarbia.

Hypercarbia is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous product of the body’s metabolism and is normally expelled through the lungs.

Hypoxia is the absence of enough oxygen in the tissues to sustain bodily functions.

The belief is infants who sleep on their tummy, or on soft bedding, use a blanket, have stuffed toys in their crib, have bumper pads attached to their cribs, sleep on foam filled surfaces such as coaches and chairs, sleep with others, or have anything close to their face (including their hands and arms), that can trap their carbon dioxide (exhaled air), they are at a higher risk of SIDS or SUID. 

When infants sleep on their back with no blanket, there is a much lower risk of anything being able to trap carbon dioxide – making it less likely for an infant to continually rebreathe his exhaled air.

For infants to safely tummy sleep, we need to remove the risk of trapping carbon dioxide which is impossible with traditional crib mattresses since they contain fillers, vinyl coatings, quilted tops, or need solid coverings to avoid contamination. These fabrics and fillers all trap potentially lethal carbon dioxide.

Why Some Infants Who Tummy Sleep Are at Higher Risk

Most of us know, or can empathize with, the scary feeling of having a heavy blanket or pillow over our faces that forces a natural trigger to remove the object blocking oxygen.  We also don’t worry about sleeping on our big fluffy pillows, pillow-top mattresses with our down quilts because we have an innate sense to turn our heads or move, even if in a deep sleep, if our breathing is labored or heavy because of the build up of carbon dioxide. 

Like adults, most infants will turn their head or fight to get something off their face when carbon dioxide begins to cause breathing difficulties.  But sadly, some infants don’t!

In 2010, a group of scientists discovered the first direct correlation between SIDS/SUID deaths and serotonin levels by studying the brain stems of infants who had died suddenly and unexpectedly.    Serotonin is a brain chemical that conveys messages between cells and plays a vital role in regulating breathing, heart rate, and sleep.  These researchers theorize that this newly discovered serotonin abnormality may reduce infants’ capacity to respond to breathing challenges, such as low oxygen levels or high levels of carbon dioxide.  The lead scientist states, “These high levels may result from re-breathing exhaled carbon dioxide that accumulates in bedding while sleeping face down.”

 Multiple other studies have followed linking high levels of serotonin in blood levels of SIDS infants and deficiencies in serotonin receptors.  All these studies report a common outcome; reflex apnea and arousal responses resulting in an infant’s inability to respond to rebreathing of carbon dioxide.  In short, some infants just do not respond when in danger of rebreathing their exhaled air!

Even though this link between serotonin and SIDS/SUID was a major finding in 2010, over ten years later, we still have no way to test live infants to determine their serotonin levels, serotonin abnormalities, reflex apnea, or arousal responses.  Consequently, all infants are at risk of rebreathing lethal levels of carbon dioxide if they tummy sleep or are in an unsafe sleep environment.

Subsequent studies have focused on how deficits in the hypothalamus region of the brain may cause the lack of response of infants to carbon dioxide rebreathing. 

The brainstem and hypothalamus are two regions housing nuclei with important roles in stress responses and arousal mechanisms.

Since deaths attributed to SIDS occur during sleep, failure to arouse in a stressful situation comprises one component in the proposed mechanism of death.  The hypothalamus is a small but complex part of the brain with important roles in the homeostasis of energy balance, circadian rhythms, and stress responses, as well as growth and reproductive behaviors. As a regulatory center for so many functions, it receives input from, and transmits output to, a large number of other brain regions. Thus, as the hypothalamus controls many physiological functions, and is highly interconnected with other brain regions, it is an excellent candidate for abnormalities contributing to the pathogenesis of SIDS.

Rebreathing of carbon dioxide continues to be a major concern for safe infant sleep since it leads to:

  • Asphyxia
  • Hypercarbia
  • Hypoxia

Dangerous Advice

I continually read recommendations by medical professionals and popular pregnancy resources with one common theme; once your baby can rollover, they are safe to sleep on their tummy.  For example, Community Baby Center, a credible baby forum sponsored by Johnson & Johnson, states, “Once your baby is strong enough to roll from back to front and front to back by himself, you don’t need to worry about him rolling onto his stomach during sleep.”

Parents Magazine states, “If your baby is able to flip himself onto his stomach while sleeping, it’s okay to leave him that way.”  Unfortunately, this is dangerous advice.

Researches out of New Zealand report, “Parents and caregivers are frequently concerned about the appropriate strategy for infants who have learned to roll over, which generally occurs at 4 to 6 months of age.  As infants mature, it is more likely that they will roll.  In one study, 6% and 12% of 16- to 23-week-old infants placed on their backs or sides, respectively, were found in the prone (face down) position; among infants aged 24 weeks or older, 14% of those placed on their backs and 18% of those placed on their sides were found in the prone position.  Repositioning the sleeping infant to the supine (back) position can be disruptive and might discourage the use of supine position altogether.  Data to make specific recommendations as to when it is safe for infants to sleep in the prone position are lacking.

This research shows that over one quarter of the infants who died of SIDS in the prone (tummy) position in their study were last placed non-prone (on their back). These researchers suggested that an infant’s competence in escaping from potentially lethal situations during prone sleep may be impaired by inexperience in prone sleeping.  Their findings were later supported by Dr. Moon (Head of AAP Safe Sleep Task Force) and colleagues in their review of infant sleep related deaths in childcare settings.   Unfortunately this infant inexperience in prone sleep is now a common unintended consequence of the successful back-to-sleep campaign – babies who roll and are not used to sleeping on their tummy are at greater risk of SIDS when sleeping on conventional crib mattresses with fiber fill.  Babies who never sleep on their stomachs don’t learn behaviors that may lessen their risk of SIDS, researchers at Washington University School of Medicine in St. Louis have found. Even so, the researchers caution that infants should always be placed on their backs to sleep.

“The first few times babies who usually sleep on their backs or sides shift to the prone (lying face down) position, they have a 19-fold increased risk of sudden death,” says senior author Bradley T. Thach, M.D., a Washington University pediatrician at St. Louis Children’s Hospital. “We wondered if these babies, finding themselves face down, fail to turn their heads to breathe easier. If so, is that because their reflexes haven’t developed far enough or because they just don’t wake up?”  The findings also indicate that good head-lifting ability while lying prone may not be sufficient to protect a baby from SIDS. “Many parents think that if a baby can lift its head, he or she is okay to sleep prone, but that is a false assurance,” Thach says

Dr. Brad Thach, now retired, spent most of his career as a SIDS researcher.  His research is still considered relevant.  He and Dr. James Kemp are credited with finding the link between rebreathing carbon dioxide and SIDS.

About Safe Sleep Policy Makers

Who are AAP Policy Makers?  The American Academy of Pediatrics (AAP) Committee on Fetus and Newborn established the AAP’s Safe Sleep Task Force back in the 90’s and currently oversees their work.  The AAP Safe Sleep Task Force Members are the ones who write the AAP’s safe sleep policies and guidelines.  The Task Force is comprised of five physicians who volunteer their time and expertise trying to make sense of the available data. Unfortunately, these scientists are not without their biases.  For example, prior to the 2016 updated policy, a new physician was added that specializes in breastfeeding.  You will find a new heightened awareness to the 2016 policy outlining the importance of breastfeeding to reduce the risk of SIDS even though there are no gold standard scientific studies to support breastfeeding as a way to prevent SIDS/SUID.

The AAP, including the Safe Sleep Task Force, does not endorse, certify, or recommend specific products.  In fact, the AAP restricts interactions with manufacturers, making it difficult for manufacturers to ensure their products are safe for consumer use. 

Randomized Case Controlled Studies vs. Retrospective Analysis

The AAP safe sleep policies are based heavily on retrospective analysis such as infant death scene investigations which can be flawed.  Actual scientific testing is not conducted to prove SIDS theories because unethical testing would be required.  The closest testing showing rebreathing of carbon dioxide as a probable cause of SUID/SIDS was done by Dr. James Kemp who used baby bunnies

The AAP Safe Sleep Task Force members use retrospective analysis to create safe sleep recommendations.  This means, the best data they have is to sift through thousands of infant death reports and find correlations of infants in a certain age group, gender, weight, etc. and try to determine why some infants lived and others died.  For example, let’s take the “back-to-sleep” recommendation.  These scientists found that infants fitting similar profiles were more likely to die if they were on their tummy while sleeping than on their back.

Retrospective analysis data can often be flawed, and it is subject to interpretation by the scientists.  Death scene investigations are not always standardized.  There is a significant effort in this direction, but we are not there yet.  It is up to the medical examiner or pathologist to determine the cause of death and take notes on the series of events and the scene.  You can have two examiners look at the same scene, and there is a high probability one examiner will include certain data and exclude data the other examiner would not.  Often examiners will label a death as SIDS if they infant was sleeping during the incident.

Limitations of Safe Sleep Policy Makers

The absence of Randomized Case Controlled (Gold Standard), means recommendations are based on retrospective analysis.   For example, it is recommended not using blankets for infants and instead put infants to sleep in wearable blankets or blanket type sleepers.  No scientific studies exist to conclusively show if a wearable blanket will prevent SIDS deaths.  However, many death scene investigations revealed that infants who died compared to infants in a similar setting who did not, had loose blankets in their cribs, suggesting they are at an increased risk for SIDS.  The same goes for back sleeping.  No gold-standard scientific studies have been conducted to show if an infant is at increased risk of dying if on their tummy. However, retrospective data shows infants who were on their back were much less likely to die during sleep, suggesting back sleep reduces the risk for SIDS.

Unfortunately, some safe sleep advocates have approached the safe sleep guidelines as literal and precise rules, not open for interpretation or consideration.  This was not and cannot be the intended use of these guidelines due to their inherent scientific limitations.  Pediatricians, parents and safe sleep advocates need to realize that the guidelines are just that—guidelines.

SIDS and Crib Mattresses

Most of us know the importance of keeping fresh oxygen flowing to a sleeping baby and avoid anything in the crib that can block fresh oxygen or cause the build-up of carbon dioxide and heat.  

The FDA (Food and Drug Administration), the CPSC (Consumer Product Safety Commission) and the AAP all warn parents of infant to keep soft objects and loose bedding out of the crib to reduce the risk of SIDS, suffocation, and entrapment, and strangulation: “Soft objects, such as pillows, quilts, comforters, sheepskins, bumper pads, stuffed toys, and other soft objects should be kept out of an infant’s sleeping environment. Loose bedding such as blankets and sheets may be hazardous.  These conditions are all unsafe sleep conditions for infants.” 

Unfortunately, conventional crib mattresses with fiber fill, vinyl covers, and quilted toppers all impede the flow of fresh oxygen, cause carbon dioxide to accumulate and artificially elevate an infant’s core body temperature if an infant is sleeping on their tummy. 

According to Dr. James Kemp and Dr. Brad Thach, these bedding materials act to retard the dispersal of exhaled gasses (carbon dioxide), retaining the gasses near a face down infant’s mouth. With each subsequent breath, the infant takes in an air mixture which is progressively less adequate to sustain life. The more conducive an item is to rebreathing (retaining carbon dioxide), the more hazardous the item would be.

Most SIDS experts agree, Infants sleeping on their tummy on fiberfill crib mattresses, quilted surfaces, soft surfaces, pillow-like surfaces, vinyl pads, mattresses filled with tea tree bark and other natural fibers, and even surfaces that claim to be breathable, show increased risk of rebreathing of carbon dioxide. 

Safe Infant Sleeping in the Prone (Face-Down) Position

In the 2011 AAP Safe Sleep Policy and Technical Report, the Task Force Members state, “play yards and bassinets with vertical sides made of air-permeable material may be preferable to those with air-impermeable sides.” The recommendation to include air permeable sides in play yards and bassinets is based on the retrospective studies of the AAP’s Chairperson of the Safe Sleep Task Force, Dr. Rachel Moon and her colleague Dr. Jody Pike

According to Moon and Pike, “We performed a retrospective review and analysis of deaths in bassinets occurring between June 1990 and November 2004 that were reported to the CPSC.”  Moon and Pike noted several infants who had died where discovered with their faces close to or pressed up against the side of the bassinet or play yard.   

In 2010, a pediatrician and her sister began to challenge the AAP’s Safe Sleep Task Force Members to include published studies confirming the safety benefits of air-permeable crib mattresses and sleep surfaces for infants who were in a face-down position.  After all, they were recommending air permeable sides in bassinets.

Finally, in 2016,  Safe Sleep Policy Makers state, “Certain crib mattresses have been designed with air-permeable materials to reduce rebreathing of expired gasses, in the event that an infant ends up in the prone position during sleep, and these may be preferable to those with air-impermeable materials.”

So, When is it Safe for Your Baby to Sleep on Thier Tummy? 

Based on what we know:

  • Why back sleeping is best if your infant is sleeping on a traditional crib mattress with fiber fill or quilted surfaces.
  • We currently have no way to determine which infants who tummy sleep or roll over are at higher risk.
  • If your baby can roll over on their own from back to tummy and tummy to back, they are “safe” to tummy sleep – is not only bad advice it could prove fatal.
  • Who our safe sleep policy makers are and the scientific limitations they face.
  • The issues with conventional crib mattresses that contribute to unsafe sleep conditions.
  • The safety benefits of air permeability.

Based on research, there is no clear age marker or milestones when it is safe for an infant to tummy sleep.  However, there are “air permeable” alternatives to conventional crib mattresses recognized by the AAP’s Safe Sleep Task Force that significantly eliminate the risks associated with tummy sleeping on crib mattresses with fiberfill and artificial cores.  One of these crib mattresses, currently available in the US, was included in the scientific studies used by the AAP to recognize the safety benefits of “crib mattresses designed with air-permeable materials to reduce rebreathing of expired gasses, in the event that an infant ends up in the prone position during sleep, and these may be preferable to those with air-impermeable materials.”

 Back sleeping is safest, but if your baby insists on tummy sleeping, make sure they are sleeping on an air permeable crib mattress.  If you want to learn more about air permeable crib mattresses that allow an infant to breathe normally even if face straight down, check out the completely breathe-through crib mattress by SafeSleep®.

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