Tuesday, October 4, 2011

Sudden Infant Death Syndrome linked to tobacco smoking during pregnancy

What is Sudden Infant Death Syndrome (SIDS)?

Sudden Infant Death Syndrome (SIDS) is a medical term that describes the sudden death of an infant which remains unexplained after all known and possible causes have been carefully ruled out through autopsy, death scene investigation, and review of the medical history. SIDS is responsible for more deaths than any other cause in childhood for babies one month to one year of age, claiming 150,000 victims in the United States in this generation alone - 7,000 babies each year -nearly one baby every hour of every day. It strikes families of all races, ethnic and socioeconomic origins without warning; neither parent nor physician can predict that something is going wrong. In fact, most SIDS victims appear healthy prior to death.

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Causes and Risk Factors

The cause of SIDS is unknown. Many doctors and researchers now believe that SIDS is caused by several different factors, including:
  • Problems with the baby's ability to wake up (sleep arousal)
  • Inability for the baby's body to detect a build-up of carbon dioxide in the blood

SIDS rates have dropped dramatically since 1992, when parents were first told to put babies to sleep on their backs or sides to reduce the likelihood of SIDS. Unfortunately, SIDS remains a significant cause of death in infants under one year old. Thousands of babies die of SIDS in the United States each year. SIDS is most likely to occur between 2 and 4 months of age. SIDS affects boys more often than girls. Most SIDS deaths occur in the winter.

The following have been linked to a baby's increased risk of SIDS:
  • Sleeping on the stomach
  • Being around cigarette smoke while in the womb or after being born
  • Sleeping in the same bed as their parents (co-sleeping)
  • Soft bedding in the crib
  • Overheating from excessive sleepwear and bedding.
  • Multiple birth babies (being a twin, triplet, etc.)
  • Premature birth
  • Having a brother or sister who had SIDS
  • Mothers who smoke, drink alcohol, or use illegal drugs, while pregnant
  • Poor prenatal care
  • Being born to a teen mother
  • Short time period between pregnancies
  • Slower-than-normal growth rate
  • Late or no prenatal care
  • Living in poverty situations
  • Low Apgar score at birth (An Apgar score measures a baby's overall condition and is taken soon after a baby is born. It is based on the baby's skin color, breathing, heart rate, responsiveness, and muscle tone.)

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While studies show that babies with the above risk factors are more likely to be affected, the impact or importance of each factor is not well-defined or understood.

Stomach Sleeping

Foremost among these risk factors is stomach sleeping. Numerous studies have found a higher incidence of SIDS among babies placed on their stomachs to sleep than among those sleeping on their backs or sides. Some researchers have hypothesized that stomach sleeping puts pressure on a child's jaw, therefore narrowing the airway and hampering breathing.

Another theory is that stomach sleeping can increase an infant's risk of "rebreathing" his or her own exhaled air, particularly if the infant is sleeping on a soft mattress or with bedding, stuffed toys, or a pillow near the face. In that scenario, the soft surface could create a small enclosure around the baby's mouth and trap exhaled air. As the baby breathes exhaled air, the oxygen level in the body drops and carbon dioxide accumulates. Eventually, this lack of oxygen could contribute to SIDS.

Also, infants who succumb to SIDS may have an abnormality in the arcuate nucleus, a part of the brain that may help control breathing and awakening during sleep. If a baby is breathing stale air and not getting enough oxygen, the brain usually triggers the baby to wake up and cry. That movement changes the breathing and heart rate, making up for the lack of oxygen. But a problem with the arcuate nucleus could deprive the baby of this involuntary reaction and put him or her at greater risk for SIDS.

Tobacco Smoking and SIDS

Multiple studies have shown a strong causal relationship between maternal smoking and the Sudden Infant Death Syndrome (SIDS). Researches vary in size and methodology but consistently demonstrate significantly increased odds of SIDS with both prenatal and postnatal maternal smoking. Babies born to mothers who smoked during pregnancy are twice as likely as other babies to die of SIDS. Actually, about 24% of SIDS deaths are considered to be related to smoking during pregnancy. Scientists don't fully understand exactly why babies born to mothers who smoke have an increased risk of SIDS, but part of the problem may be that these babies are harder to wake up when they're sleeping, a situation that may be linked to SIDS.

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Sleep Apnoea

Hugo Lagercrantz, one of the researchers at the Karolinska Institute in Stockholm, Sweden says: "I think it is most dangerous to smoke during pregnancy, because nicotine may set the sensors that detect low oxygen levels wrongly. The key is a membrane protein in nerves, one of several that bind acetylcholine, an important transmitter of neural signals. One particular form of the receptor is also strongly activated by nicotine. The Swedish scientists, with colleagues in France, studied the breathing of sleeping mice with and without this form of the receptor.

Sleeping people stop breathing several times during the night, an event called sleep apnoea. Normally the resulting fall in blood oxygen partially wakes you, and breathing resumes. In SIDS babies, this response fails. It also failed in the mutant mice during research, meaning the receptor is needed to help detect low blood oxygen and re-start breathing after sleep apnoea. Prolonged exposure to nicotine is known to desensitise the receptor, so exposure before birth might make the system less sensitive, and less likely to rouse a baby after sleep apnoea.

Another response to low oxygen is deeper breathing. But observation of the mice shows that nicotine dampens this directly, further reducing the ability to recover from sleep apnoea.

Oxygen Deprivation

Researchers at McMaster University have found a mechanism that better explains SIDS mechanism, in terms of how it is affected by tobacco exposure, or why an infant's ability to respond to oxygen deprivation after birth--or a hypoxic episode--is dramatically compromised by exposure to nicotine in the womb, even light to moderate amounts.

"While cigarette smoke contains many different compounds, we found there is a direct impact of one component, nicotine, on the ability of certain cells to detect and respond to oxygen deprivation," says Josef Buttigieg, lead author and a PhD graduate student in the department of Biology. "When a baby is lying face down in bed, for example, it should sense a reduction in oxygen and move its head. But this arousal mechanism doesn't work as it should in babies exposed to nicotine during pregnancy."

The research, which was conducted on laboratory rats in collaboration with Dr. Alison Holloway, explains the critical role that catecholamines--a group of hormones released by the adrenal glands--play in a baby's transition to the outside world.

During birth, the baby is exposed to low oxygen, which signals the adrenal glands to release the catecholamines, which contain adrenaline, or the 'fight or flight' hormone, explains Buttigieg.

It is these catecholamines that signal the baby's lungs to reabsorb fluid, to take its first breath, and help the heart to beat more efficiently. And for some months after birth, the adrenal gland still acts as an oxygen sensor, aiding in the baby's arousal and breathing responses during periods of apnea or asphyxia. But the ability to release catecholamines during these moments--a critical event in the adaptation of life outside the womb--is impaired due to nicotine exposure.

"At birth, the nervous control of the adrenal gland is not active and so a baby relies on these direct oxygen sensing mechanisms to release catecholamines," says Colin Nurse, academic advisor on the study and a professor in the department of Biology. "But nicotine causes premature loss of these mechanisms, which would normally occur later in development after nervous control is established. Thus, the infant becomes much more vulnerable to SIDS."


While the prenatal baby exposure to tobacco is the leading factor of the potential risk for the newborn baby, the certain increased danger to the baby health has also been reported from the exposure to tobacco smoke after birth. So, think twice before continuing smoking during pregnancy and at the early years of your baby, as the consequences might be fatal. Think twice….

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