By Dr. William Sears, M.D.
Excerpted with permission from New Beginnings, Vol. 16 No. 3, May-June 1999, pp. 68-70.
Sudden infant death syndrome (SIDS), also known as crib death, is one of the most tragic of all nighttime crises. A healthy infant is put to bed and is later found dead for no apparent reason. Parents are devastated, left wondering why, and while medical research has produced a number of theories about SIDS, it still cannot explain exactly what happens when an infant dies unexpectedly during sleep.
Newer studies, however, suggest that various factors that are under parents' control influence SIDS risk. While you cannot guarantee that your baby will not become a SIDS victim, you can lessen the chances. I have come to believe that practicing the attachment style of nighttime parenting is one of the most important things you as a parent can do to lower the risk of SIDS in your baby.
SIDS and Breathing Mechanisms
Because the infant dies during sleep, SIDS can be thought of as a sleep disorder. The infant who becomes a SIDS victim may be unable to control his breathing automatically during sleep or to arouse from sleep in response to a breathing problem. In order to understand this theory of SIDS causation it is first necessary to understand how the infant normally continues breathing while sleeping.
In order for the body to function there must be a balance of just the right amount of oxygen and carbon dioxide in the blood. In order to maintain this balance, tiny sensor cells called chemoreceptors are located along some major blood vessels. During sleep, the body is particularly dependent on these chemoreceptors to keep breathing going.
In the first few months, the infant's automatic breathing mechanisms are immature. When watching a sleeping baby breathe, you will notice that his breathing lacks a regular pattern. Periodically he appears to stop breathing, sometimes for as long as ten to fifteen seconds, and then self-starts without any apparent problem. This is called periodic breathing and is normal for the tiny infant. The younger or the more premature the baby, the more irregular the breathing pattern and the more noticeable the periodic breathing. As the baby matures (around six months), breathing patterns during sleep become more regular and periodic breathing lessens. The episodes when the baby stops breathing are called apnea. Sometimes they are prolonged for more than fifteen to twenty seconds, and the heart rate drops significantly (greater than twenty percent). As a response to this sleep apnea, either automatic start mechanisms click on or the infant awakens. Either way, normal breathing resumes.
Sometimes the apnea is prolonged, and breathing fails to start again. Infants who are hooked up to apnea monitors show signs that the oxygen in the blood is at a dangerously low level: the heart rate becomes alarmingly slow, and the infant turns pale, blue, and limp. An observer must intervene and arouse the infant. Sometimes a simple touch will trigger the self-starting mechanism; sometimes the infant must be aroused from sleep in order to breathe; sometimes mouth-to-mouth resuscitation is necessary to initiate breathing again. Infants who have experienced an apnea episode that required outside intervention to restart their breathing are called near-miss SIDS. In other words, they would have died had someone not intervened. Tragically some infants stop breathing permanently, succumbing to SIDS.
SIDS as a Sleep Disorder
The peak incidence of SIDS is around three months, which coincides with the time most babies begin to sleep “better,” that is, to spend a larger percentage of sleep time in quiet sleep. During quiet sleep, infants are less responsive to the breathing-stimulating effects of low oxygen and increased carbon dioxide (Harper 1982).
In addition, studies of near-miss infants and siblings of SIDS infants show that these babies have fewer night-waking episodes. In the first few months, infants normally have frequent periods of night-waking as they ascend from quiet sleep to active sleep and back into quiet sleep. Researchers have suggested that arousal from sleep may be essential for resumption of breathing in babies who have less effective self-starting mechanisms (Harper 1981). Difficulty with waking up may place infants at higher risk for SIDS. Infants presumed to be at high risk for SIDS also show more frequent episodes of sleep apnea and periodic breathing (Guillemmault 1981). This apnea occurs most frequently between 1:00 AM and 6:00 AM and within ten minutes of awakening. The infants who woke most often at night had fewer episodes of apnea. Active sleep guards against SIDS. Sleep studies have shown that the onset of active sleep (REM sleep) stimulates breathing and heart rate. On the basis of their studies, researchers hypothesized that active sleep “protects” human infants from SIDS. The peak risk period for SIDS coincides with the rapid decrease in active sleep between two and three months of age. By six months of age, cardiopulmonary compensatory mechanisms in quiet sleep are more mature and the risk of death (from failure of these mechanisms) is reduced (Baker and McGinty 1977).
In other words, infants are not designed to sleep through the night until they're mature enough to do so safely.
SIDS and Breastfeeding
For many years, SIDS researchers maintained that there was no difference in the incidence of SIDS between breastfed and artificially fed babies, but newer studies have shown that infants who were never breastfed may have two to three times the risk of dying of SIDS. Breastfeeding's protective effect has been confirmed by research in New Zealand (Mitchell 1991), England (Fleming 1994), and the United States (Hoffman 1988). There are a number of possible explanations for the lowered risk of SIDS in breastfed babies. Breastfeeding protects infants from respiratory and gastrointestinal infections, and these have been shown to contribute to SIDS risk. Human milk enhances the development of the central nervous system, providing vital nutrients for the process of myelination, the development of an insulating sheath around nerves. Better brains may provide babies with better respiratory control during sleep. Breastfed babies sleep less soundly than artificially fed infants and are more likely to sleep with their mothers; thus, they may be more easily aroused when they experience a stop-breathing episode. While SIDS does occur in breastfed babies, breastfeeding is one way of lowering the risk.
How Parenting Style Can Decrease the Risk of SIDS
What are the practical implications of this research for nighttime parenting? In the 1984 edition of NIGHTTIME PARENTING I proposed the following hypothesis:
In those infants at risk for SIDS, natural mothering (unrestricted breastfeeding and sharing sleep with baby) will lower the risk of SIDS.
This was a new idea at the time, one that I based upon my reading of SIDS research and my understanding of the close relationship between a breastfeeding mother and her baby. My hope was that publication of this hypothesis would stimulate more scientific research in this area. Fifteen years later, in 1999, I am happy to report that the body of evidence available to support my original idea is growing, and experts are beginning to understand how a mother's presence with her baby during sleep can help to prevent SIDS. Here's the reasoning behind my theory - and the evidence and ideas that support it.
Sharing Sleep May Lower SIDS Risk
If SIDS is related to a diminished arousal response during sleep in some infants, it follows that anything that increases the infant's sensitivity or the mother's awareness of her baby may decrease the risk of SIDS. This is exactly what sharing sleep and night nursing do.
As a father of several all-night nursers, I have noticed that mother and baby often stir or awaken briefly at the same time. The nursing pair have a heightened awareness of each other. A study of mothers and babies co-sleeping in a sleep laboratory has documented the shared awakenings of co-sleeping, breastfeeding mothers and babies (McKenna 1994). When one stirred, coughed, moved, or changed positions, so did the other. The researchers also demonstrated that co-sleeping mothers and babies were often in the same stage of sleep during the night. Clearly, the presence of each affects the other.
Interestingly, anthropological studies have shown that the rate of SIDS is approximately three to four times higher in cultures where mothers do not sleep with their babies. More extensive research is needed on exactly what happens when mother and baby sleep close to each other. It seems odd that science demands proof that co-sleeping is good for babies, since mothers and babies sharing sleep has been the norm through most of human history, but there is still much to learn about how mothers help their babies develop. Meanwhile, I have to ask, if there were fewer cribs, would there be fewer crib deaths?
Babies Breathe Better When Sharing Sleep
My interest in the relationship between shared sleep and lowered risk of SIDS led me to arrange a study involving our daughter, Lauren, when she was eight weeks old. Using sophisticated monitoring equipment in our home, a technician and I monitored Lauren's sleep on two separate nights. On one night, my wife, Martha, slept beside Lauren. On the other night, Martha nursed Lauren to sleep in our bed, but slept in an adjacent room. We found that Lauren's heart rate and her breathing were more regular during shared sleep, with far fewer low points in blood oxygen levels. Monitoring another mother-infant pair produced similar results.
Obviously, this was a very small sample group, from which it is impossible to draw statistically valid conclusions. However, it does suggest a theory that needs further testing: a baby who sleeps next to mother is likely to experience fewer apnea episodes and thus may be at lower risk for SIDS. While again, this is not scientifically tested evidence, I have had many breastfeeding and co-sleeping mothers in my practice tell me that they have noticed that their infants breathe more rhythmically lying next to mother in bed than they do in a crib. One mother, whose baby was monitored with an apnea monitor during sleep because of breathing difficulties, found that the alarm went off frequently when the baby slept alone, but not at all when the baby slept with mother.
If SIDS is related to a baby’s inability to arouse himself from sleep, it follows that babies are simply not designed to sleep through the night until they are mature enough to avoid respiratory failure during quiet sleep. Parents need to be aware that studies which show that babies sleep through the night at a given age were performed in artificial settings: a sleep laboratory, a hospital, or some other nighttime environment in which baby sleeps alone. Sleeping alone is considered the norm, so babies are studied sleeping alone in cribs. The conclusions drawn from these studies of “normal” sleeping infants are that infants begin to have a higher proportion of quiet or non-REM sleep and sleep in longer stretches ("through the night") by three months of age - incidentally, the peak age for SIDS. From erroneously set-up experiments come erroneous norms. Parents (and doctors) should not use these norms as a justification for training babies to sleep through the night at a given age.
One study suggests that the sleep norms extracted from these studies that babies sleep through the night by six months of age may be attributed to the early weaning and separate sleeping practices of Western culture (Elias,1986). Researchers compared sleep/wake patterns in infants reared with two different parenting styles. One group consisted of sixteen mother-infant pairs, called the standard care group, who breastfed but tended to wean earlier and sleep separately. The other was made up of sixteen mother-infant pairs from La Leche League. These pairs breastfed more frequently throughout the day, weaned later, and usually slept together. Sleep/wake patterns developed differently in the two groups of infants. The sleep periods of the infants in the standard care group increased in duration from a median of 6.5 hours at two months to 8 hours at four months of age. The sleep periods of infants in the La Leche League group never increased from the median of four hours; they continued to awaken at night throughout the period of study.
These researchers also showed that the combination of nursing and sharing sleep had the greatest effect on sleep patterns. Babies who nursed and shared sleep with their mothers slept shorter stretches at a time; those who nursed but did not share sleep slept longer; and babies who neither nursed nor shared sleep slept the longest.
The human infant is meant to be a continuous contact species. The composition of milk of each species gives a clue to the infant care practices natural to that species. Animals who leave their young for extended periods produce a milk high in fat and protein which satisfies the young for a relatively long period of time between feedings. Human milk is relatively low in fat and protein, necessitating frequent, seemingly continuous nursing. The human infant is meant to be carried in arms during the day and nestled with mother in bed at night - not trained into a separate sleeping arrangement before he is ready.
A Final Word
While I believe that there is much parents can do to lower the risk of SIDS in their infant, I do not mean to suggest that parents of a baby who dies of SIDS are in any way at fault. SIDS is a terrible tragedy, and it is not entirely preventable.
For additional information on how attachment parenting can lower the risk of SIDS, see Dr. Sears' book, Nighttime Parenting, published by La Leche League International.
For more information on the research of healthy baby sleep, see the links on this page.
Baker, T. L. and McGinty, D. J. 1977. Reversal of cardiopulmonary failure during active sleep in hypoxic kittens: Implications for sudden infant death. Science 198:419.
Carpenter, R. G. and Emory, J. L. 1977. Final results of study of infants at risk of sudden infant death. Nature 268:724.
Elias, M. F. 1986. Sleep-wake patterns of breastfed infants in the first two years of life. Pediatrics 77:332-39.
Fleming, P J. 1994. Proceedings of the Fourth Annual SIDS Alliance National Conference, Orlando, FL, November 9-12.
Guillemmault, C. et al. 1981. Sleep parameters and respiratory variables in near-miss sudden infant death syndrome infants. Pediatrics 68:354.
Harper, R.M. et al. 1981. Periodicity of sleep states is altered in infants at risk for the sudden infant death syndrome. Science 213: 1030.
Harper, R. M. et al. 1982. Developmental patterns of heart rate and heart rate variability during sleep and waking in normal infants and infants at risk for the sudden infant death syndrome. Sleep 5:28.
Hoffman, H. et al. 1988. Risk for SIDS: Results of NICHD SIDS cooperative epidemiological study. Ann NY Acad Sci 533:13-30.
Keens, T. G. and Van der Hol, A. L. 1984. Use of hypoxic and hypercarbic arousal responses in evaluation of infant apnea. Perinatol Neonatol 8:32.
McKenna, J. J. and Mosk, S. S. 1994. Sleep and arousal, synchrony and independence, among mothers and infants sleeping apart and together (same bed): An experiment in evolutionary medicine. Acta Paediatr Suppl 397:94-102.
Mitchell, F. A. eta1. 1991. Results of the first year of the New Zealand cot death study. NZ Med 104:7.