Professor Ed Mitchell
SUDI Academic Expert
Auckland University

Ed Mitchell qualified at St George’s Hospital Medical School in London and has worked in the UK, Zambia and New Zealand.

He was the Cure Kids Professor of Child Health Research at the University of Auckland from 2001 to 2015 and is now a Professorial Research Fellow. He has published over 400 original papers, particularly on the epidemiology of sudden infant death syndrome (SIDS). He was awarded a Doctor of Science for his work on “The Epidemiology and Prevention of SIDS” by the University of London. He has received several awards for his landmark studies of SIDS and in 2009 was made a fellow of the Royal Society of New Zealand.

You have advised that parents do not sleep with their baby. Why is that?

Many studies have shown that sleeping with baby on the same sleeping surface, usually a mattress, increases the risk of sudden unexpected death in infancy (SUDI). Indeed over 50% of SUDI cases now occur in a bed sharing situation. There are certain factors that increase the risk further. These include the first 3-4 months of life, whether or not the mother smoked in pregnancy, whether she took drugs or alcohol before sleeping with the baby or was excessively tired and whether the baby was vulnerable, such as low birthweight or preterm. Even without these additional risks bed sharing increases the risk 3-fold, so our advice is “For the first six months, the safest place for baby to sleep is in a cot in the parent’s bedroom.”

bed sharing
What is about bed sharing that causes SUDI?

We believe the mechanism is accidental suffocation. The nose of the baby is soft and can easily be compressed. Also the jaw can be pushed back and occlude the airway. A healthy baby will arouse (wake up) and wriggle, but if mother has taken drugs or alcohol she won’t be responsive to this. Also if the baby has been exposed to smoking when in the womb, the arousal mechanisms are blunted, and the baby may not wake up.

smoking, bed sharing, cause
Is it safe to leave babies to sleep in car seats/capsules for extended periods of time as sometimes parents don't want to wake baby after traveling?

Babies will often fall asleep in a car seat when travelling. Not surprisingly it is tempting to leave the baby asleep in the capsule when they arrive home. But is it safe? Studies of babies in car seats show that their head may flop forward and cause partial airway obstruction and hypoxia (low oxygen levels). This will briefly wake baby up (micro-arousals). Despite these concerns, SUDI in a car seat is rare. In the 3-year Nationwide SUDI Study there was only 1 death (out of 137) that occurred in a car seat. In comparison there were 7 control (living) babies (out of 249) in a car seat during the comparison sleep. This suggests it isn’t dangerous in healthy babies, but I would be concerned about repeated hypoxia in low tone babies, such as those with Down syndrome.

car seat, car, sleep
Should we be putting a hat on baby to sleep at night now its’ got cold?

Questions relating to type and amount of baby clothing are frequent. In the original New Zealand Cot Death Study (1987-1990) baby hats (e.g. beanies and bonnets) were used in 8.3% of cases and 5.2% of controls. In the Nationwide SUDI Study hats were used by 4.8% of cases and 3.9% of controls. These differences are small and not statistically significant.

In infants the surface area of the head and neck is 20% of their total body area (compared with just 9% in adults). Heat loss can be considerable, so in cold conditions a hat will reduce this. This may prevent the baby getting cold and uncomfortable. But it doesn’t affect the risk of SUDI.

Head covering increases the risk of SUDI, but this does not refer to hats; it refers to baby’s head being covered with blankets. A meta-analysis of 10 studies found the prevalence in cases was 24.6% and 3.2% among controls. This suggests head covering by blankets is a modifiable risk factor associated with SIDS deaths and has led to the UK recommendation to place baby at the foot of the bed (“Feet to foot”). Theoretically this might prevent babies kicking the blankets over their heads, but there isn’t much evidence to support that this happens, which is why we do not emphasise this in New Zealand.

hat, cold, baby clothing
What is the difference between SUDI and SIDs and why the terms have changed from "cot death" as it was previously known?

Sudden infant death syndrome (SIDS) has been present since antiquity. Indeed it is described in the Old Testament of the Bible: 1 Kings 3:19 ‘‘And this woman’s child died in the night.’’ “Cot death” was well known to pathologists, but not to paediatricians as they never saw them, as the deaths occurred in the home. These deaths were often labelled as pneumonitis (inflammation of the lung). It was not until 1965 that a specific International Classification of Diseases (ICD) code was allocated for SIDS. SIDS is the scientific term for a sudden unexplained infant death. These deaths generally occur during a sleep, and no cause is found despite a detailed examination of the death scene, medical history and thorough autopsy. Nowadays 50+% of deaths occur in a bed sharing context, so using the term “cot death” is inappropriate. The cause of deaths associated with bed sharing may be labelled as accidental asphyxia (i.e. suffocation), SIDS (that is unexplained) or unascertained (often used when the pathologist cannot distinguish between suffocation and SIDS). The trouble is that one pathologist or coroner might call the death SIDS and another accidental asphyxia. Sudden unexpected death in infancy (SUDI) captures all three causes, including unexplained and explained.

cot death, SUDI, SIDS
When is it OK for our baby to sleep with his older sibling?

Only a few studies have examined this. One of the best is the Chicago Infant Mortality Study. This case-control study found that bed sharing with siblings (with or without the parents) raised the risk fivefold.

Although observational studies do not tell us the mechanism, all parents would have observed how deeply preschool children sleep, and it would not be surprising if the sibling did not respond to the struggles (arousal) of the baby if baby was overlaid.  
However, by 6 months of age 85% of SUDI cases have occurred and after 12 months SUDI is very rare. So for the safety of your baby do not let baby sleep with an older sibling until at least 12 months of age.

What about co-bedding twins? Certainly there are SUDI deaths that have occurred in a twin when sleeping together (co-bedding), however, this practice is quite common in New Zealand, so it is difficult to estimate whether co-bedding is a risk or not, but given the increased risk of SUDI associated with sleeping with older siblings, I would recommend caution.

bed sharing, siblings
What temp is best for our baby’s room?

This simple question is actually quite complex! There is little information on the room temperature when the death occurred. Researchers have tried to estimate the room temperature from the environmental (outside) temperature, but this is difficult, especially if room heating and insulation need to be taken into account. So one has to rely on case reports. I’ve reviewed cases where the room temperature was very high, but more frequently the rooms are cold. Is this a risk from the cold or is this a marker of poor, disadvantaged families living in poorly heated and uninsulated homes? I don’t know.
Recommendations vary: 16-20°C and 20-22°C have both been recommended. Not everyone has a thermometer, so I’d recommend a temperature that is comfortable for you with a light jersey. Plunket has sensible advice on their website. They recommend:

  • the [baby’s] room is well aired with the door open, especially if you use a heater
  • the temperature should feel comfortable for a lightly-clothed adult - the temperature around the cot will be more even if it’s away from windows
  • the room is not too hot - using an electric heater with a thermostat is best (fan heaters may overheat the room and gas heaters can give off dangerous fumes)
  • the cot is away from windows, curtains, blind cords, power points and heaters.
temperature, heater
What is the difference between SIDS and SUDI? Much of the available information on Safe Sleep is geared towards preventing suffocation.

Terminology has changed over time. It was once called ‘cot death’ despite many of the deaths not occurring in the cot. It was then changed to SIDS which is unexplained infant death. SUDI (Sudden Unexpected Infant Death) is a broader term than SIDS. It includes unexplained deaths (that is SIDS) and sleep related deaths from asphyxia or suffocation, such as may occur while bed sharing. In part this change has been driven by changes in diagnostic fashion. One pathologist might call the death SIDS, another suffocation in bed while bed sharing and another unascertained. SUDI captures all the deaths that were once labelled SIDS or cot death. SIDS is by definition unexplained, and therefore cannot be predicted or prevented. However, we can predict what increases the risk and we know that the ‘Back to Sleep’ campaign and the Safe Sleep programme has and is reducing mortality. The good thing about describing the mechanism as due to suffocation is that it suffocation is obviously preventable.

asphyxia, suffocation
I am so worried about my baby dying of SUDI that I get up several times a night to check my baby. My husband tells me I shouldn’t worry.

I was sorry to hear that about your worry over SUDI. Infants of families that follow the recommended infant care practices (non-smoker, room sharing but not bed sharing, back sleeping and breastfeeding) are at very low risk of SUDI. In our recent study we calculated there would be only 6-7 deaths per year in New Zealand if these recommended advice was followed by all. This is a dramatic reduction from the 250 deaths a year that occurred in the late 1980s. There are of course some things which one cannot alter after the baby is born, such as low birthweight. We hope to implement a SUDI risk calculator which will give the absolute risk of death and identify which families need additional support.

risk, recommended
What is the difference between SIDS and SUDI? Much of the available information on Safe Sleep is geared towards preventing suffocation.

Terminology has changed over time. It was once called ‘cot death’ despite many of the deaths not occurring in the cot. It was then changed to SIDS which is unexplained infant death. SUDI (Sudden Unexpected Infant Death) is a broader term than SIDS. It includes unexplained deaths (that is SIDS) and sleep related deaths from asphyxia or suffocation, such as may occur while bed sharing. In part this change has been driven by changes in diagnostic fashion. One pathologist might call the death SIDS, another suffocation in bed while bed sharing and another unascertained. SUDI captures all the deaths that were once labelled SIDS or cot death. SIDS is by definition unexplained, and therefore cannot be predicted or prevented. However, we can predict what increases the risk and we know that the ‘Back to Sleep’ campaign and the Safe Sleep programme has and is reducing mortality. The good thing about describing the mechanism as due to suffocation is that it suffocation is obviously preventable.

Has the ‘toxic gas theory’ been proven or disproved?

This interesting theory goes back to the 1980s. It postulated that a specific fungus grew on the plastic covering of damp cot mattress. The fungus would metabolise the fire retardants in the plastic covering and would release nerves gases which could kill the baby. Proponents of the theory recommended covering the mattress with a polythene covering to stop the gases reaching the baby. To me it never seemed a likely explanation, as 50+% of deaths occurred in the parental bed, which was unlikely to be wet and contaminated with the fungus unlike the cot. The theory stimulated considerable research which was not able to replicate the gases in anything closely resembling a cot environment. In my opinion the theory was clearly wrong when it was found that the postulated nerve gases wasn’t toxic!

damp mattress, plastic covering