Below are some frequently asked questions from the CYMRC.

Why does the CYMRC not advise on the use of pacifiers (aka dummies)?

The American Academy of Pediatrics (AAP) and the CYMRC both reviewed the literature and came to the same conclusion, namely that there was a halving of the risk of sudden infant death syndrome (SIDS) with pacifier use. However, the AAP and the CYMRC came to different conclusions as to the public health message. The AAP recommends the use of pacifiers after the first month, once breastfeeding has been established. The CYMRC, however, was concerned by an Irish study that suggested that not using a pacifier in those that were used to it increased the risk (not seen elsewhere), and that there is probably an effect on breastfeeding duration, not just on initiating breastfeeding. As a result, the CYMRC decided neither to recommend or discourage its use.

What is wrong with placing a baby to sleep in the recovery position, firmly wrapped on the side for a tiny baby?

There is overwhelming evidence that for the normal full-term infant the safest position to be placed to sleep is on the back. On the front is the highest risk, and on the side intermediate risk.

This guidance is for the normal full-term infant. Preterm babies, especially those who are being ventilated, may be placed prone, however, the recommendation for such infants is to place them on their back prior to discharge home. For some babies with congenital anomalies (e.g. Pierre Robin syndrome), they need to be placed prone because they have difficulty maintaining their airway.

The recovery position is appropriate for individuals that are not conscious and, thus, have difficulty maintaining their airway. This does not apply to the normal baby who has no difficulty protecting their airway. One concern that some people have is that there is a risk of aspiration of vomitus with the back sleeping position. In fact, this is very unlikely in the normal baby. When lying on the back, the trachea is above the oesophagus so that any vomitus is more likely to be swallowed than inhaled. Further, in the normal baby, the cough reflex is maintained so a small inhalation would trigger the cough reflex that would clear the airway.

My infant resists sleeping on her back, and will turn on her side or stomach. What are the risks associated with this? Should I consider a special safe sleeping device?

If there are no other risk factors, by the time an infant is over 3 months of age, the major risk time has passed, although accidents can still happen.

Babies who can move and turn from back to front usually have the strength to ‘get out of trouble’. This is in contrast to the unaccustomed tummy sleeper who suddenly finds herself on her tummy and is in trouble.

The CYMRC has seen deaths where parents have tried to restrain their mobile babies with sheets, swaddling and devices. The ‘restrained’ baby fights the device and gets trapped in a position where it is hard to breathe and is unable to get out of it. Despite this, the CYMRC has not come out directly opposing these devices. Instead, the CYMRC would rather focus on the elements that constitute a safe sleep environment and support parents to learn to assess sleep spaces from first principles. For more information, see the CYMRC’s special report Unintentional suffocation, foreign body inhalation and strangulation here.

Keeping ahead and planning for risks that arise due to development is always a challenge. Ultimately, if your infant is over 3 months of age and there are no other risk factors, then put her down to sleep on her back and make sure that, if she does move, she cannot get herself trapped or wedged, her neck will not get flexed (feet to foot), her head will not get tangled in curtain or blind cords and the cot does not have corner posts.

Is sleeping in a pram a risk for SUDI?

Death in a pram occurs at the same frequency as might be expected in other sleeping settings, according to research data.

Most SUDI deaths occur while sleeping in cots or bed-sharing situations, and a small number of deaths also occur on sofas and couches. There is one published study that examined deaths in prams and carry-cots[1]. In this study, prams and carry-cots were used only for day sleeps. In total, 48 of the 121 cases were deaths that occurred in a pram or carry-cot. The ‘routine use’ of prams and carry-cots (used during the day for 5 or more days per week) was 40% (48/121) for cases and 43% (132/307) for controls, and this was not statistically different.

Because there is only this one published study that examines deaths in prams and carry-cots, CYMRC member and researcher Ed Mitchell asked colleagues who have run major SIDS studies for their data on cases where the deaths occurred in prams. The following table summarises the information obtained:

  Case Control
New Zealand 31/391 (7.9%) 151/1586 (9.5%)
Ireland 22/330 (6.7%) 100/1157 (8.6%)
SWISS (UK) 5/80 (6.3%) 4/87 (4.6%)
CESDI (UK) 18/319 (5.6%) 64/1296 (4.9%)
Germany 28/373 (7.5%) 89/1117 (8.0%)
Netherlands 3/136 (7.5%) 89/1117 (8.0%)
What is the difference between SIDS and SUDI?

SUDI stands for Sudden Unexpected Death in Infancy. SUDI is a broad umbrella term that includes all sudden and unexpected deaths, whether they are explained or not.

When the Police attend an unexpected infant death, they do not initially know what the cause of that death is. That is established by examining the scene, interviewing the parents/caregivers to establish the circumstances surrounding the death, and reviewing past medical history and post-mortem results (both preliminary findings and the results of any special investigations). The cause of a SUDI death[2] might include:

ICD-10 (International Statistical Classification of Diseases and Related Health Problems 10th Revision) codes
R95 Sudden infant death syndrome
R96 Other sudden death, cause unknown
R98 Unattended death
R99 Other ill-defined and unspecified causes of mortality
W75 Accidental suffocation and strangulation in bed
W78 Inhalation of gastric contents
W79 Inhalation and ingestion of food causing obstruction of respiratory tract
  Unexpected infection, cardiac and metabolic abnormalities

When an infant death is still unexplained after the circumstances surrounding the death, medical history, and post-mortem findings have been thoroughly investigated, then it is labelled Sudden Infant Death Syndrome (SIDS). However, SIDS lacks precision as a term because there is some overlap between SIDS deaths and deaths that have been potentially caused by unsafe sleeping environments. Advances in death scene and post-mortem investigations have led to more precise coding of deaths, and a shift away from classifying SIDS as a cause of death.

SIDS is defined as the sudden unexpected death of an infant less than 1 year of age, with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation, including performance of a complete autopsy and review of the circumstances of death and the clinical history.[3]

What is the likelihood that a family that has lost one infant to SIDS might lose another?

The risk of a family losing another infant to SIDS (known as the ‘recurrence risk of SIDS’ in medical terms) has been estimated to increase between 1.7 and 10.1 fold. The more robust (and larger) studies estimate a 5 fold increased risk of a recurrence after the first death. This increased risk could be due to a combination of genetic risk factors and repeating behaviours that increase the risk of SIDS.

In New Zealand, the SIDS mortality rate is 0.4 per 1000 live births[4], or 1 in 2500 live births. If the recurrence risk is 5 times the background rate, then the risk for a second SIDS can be estimated as 1 in 500.

There are many reasons for the recurrence of SIDS. Genetic research is expanding rapidly. Recent studies have identified genetic variations affecting the arousal and inflammatory systems in some SIDS cases. These variations (which are called polymorphisms) affect how well the infant is able to wake up and protect itself, but might only be lethal when combined with other external triggers, such as bed sharing or the infant sleeping on his tummy.

If most SIDS cases were due to a genetic condition alone, we would expect to see a higher recurrence rate. The risk of SIDS in twins is similar for both identical and fraternal twins[5], suggesting that an underlying genetic cause is less likely. For these reasons, it is suspected that the increased risk of recurrence of SIDS in the majority of SIDS cases is due to parents repeating practices that are now known and established risk factors. For example, a mother who smokes during each of her pregnancies will increase the risk of SIDS by 3-4 fold.

There are also several genetic abnormalities that explain a very small number of SUDI deaths, including some heart conditions (such as Long QT syndrome). Most authorities estimate that genetic abnormalities account for about 5% of cases.

What is the risk from sleeping on pillows?

Although the data are limited, the CYMRC believe it is inappropriate for adult sized pillows to be used in the first year of life and that this represents a potentially unsafe sleeping environment.

The New Zealand Cot Death Study[6] reported on the use of pillows and risk of SIDS. This is shown in the following table:

  Case: n (%) Control: n (%) Odds Ratio (95%CI)
No pillow 301 (77.6%) 1236 (81.0%) 1.0
Infant pillow 36 (9.9%) 170 (11.1%) 0.87 (0.58-1.29
Adult pillow 51 (13.1%) 120 (7.9%) 1.75 (1.21-2.51)

The study suggested that adult pillows increase risk of SIDS, but infant pillows do not. However, it did not adjust for any other potentially confounding factors so this should be interpreted with caution.

Epidemiological studies show associations, and sometimes patterns of associations can allow researchers to get a sense of the situations that are more likely to contribute to SIDS.

There are good experimental and epidemiological studies suggesting that putting an infant to sleep on his stomach on porous, soft surfaces is associated with rebreathing of air. Furthermore, Dr Shirley Tonkin has shown that some small infants in car seats flex their neck, producing obstructive apnoea, which is a narrowing of the airways at the back of the nose and in the throat. This can cause the infant to have difficulty breathing and possibly even stop breathing (apnoea). It would be reasonable to think that positioning an infant on an adult pillow might produce a similar effect that would make it difficult for the infant to breathe.[7]

Tri-pillows may also be a risk. A case series from Australia has implicated that tri-pillows may be unsafe for small infants.[8]

Is there a risk of SIDS with immunisation?

No, recent research has shown that immunisation protects infants from SIDS.

Deaths from SIDS are most common in the first few months of life, which is the same time when infants are receiving immunisations. This is why some have suggested that immunisation may be the cause of some SIDS deaths.

Several studies have examined the relationship between SIDS and immunisation. Some early studies suggested a relationship existed, but more recent studies have shown that immunisation is associated with a lower risk of SIDS. In New Zealand, for example, infants were at increased risk of SIDS if they had not received the 6 week, 3 month and 5 month immunisations. After controlling for other possible complicating factors, the risk of SIDS for non-immunised infants was twice that of infants who were immunised. Furthermore, 4.0% of SIDS cases died within 4 days of immunisation, compared with 7.6% of control infants who had been immunised within the last 4 days. There could be a reduced chance of SIDS immediately following immunisation.

The German SIDS case-control study reported similar results. This study also found that SIDS cases were immunised less frequently and later than controls. There was no increased risk of SIDS in the 14 days following immunisation. The risk of SIDS over the 14 days following immunisation was slightly lower, although this was non-significant.

An analysis of 9 case-control studies examined this relationship. Immunisations were associated with a halving of the risk of SIDS. There are biological reasons why this association may be causal, but other factors such as the healthy vaccine effect may be important.

We can be certain that immunisations are not the cause of SIDS.

Is there an increased risk of SIDS from sleeping in a car seat?

Whether or not car safety seats increase the risk of SIDS is not clearly established. There is no question that infants should be properly restrained in an approved infant car safety seat when being transported in a car because it is not possible for a parent to maintain a grip on an infant held in their arms in the event of a crash. However, a number of organisations, including the American Academy of Pediatrics, recommend that all infants born before 37 weeks should be assessed for cardiorespiratory stability in their car seat before being discharged home.

A study from Quebec[12] reviewed 508 sudden unexpected infant deaths, of which 409 were unexplained and 99 explained. A total of 17 deaths occurred in a sitting device, of which 10 were unexplained. Of these 17 deaths, 10 occurred while the infants were seated in a car safety seat, 8 of which happened during a car journey. The other 7 were in other various sitting arrangements. The difficulty in interpreting these data is that there is no control data. Without control data, we do not know the number of deaths the might be expected by chance. Therefore, we do not know whether car seats increase the risk of SIDS.

There are several studies showing that preterm infants placed in car seats experience a narrowing of the airways at the back of the nose and in the throat causing the infant to have difficulty breathing and decreased oxygen levels (known as obstructive apnoea). This has also been demonstrated in full- term infants.

Some infants who have fallen asleep in the car seat are then transported into the home and left asleep in the car seat. These infants are often warmly dressed for outdoor temperatures (and then overdressed for warmer, indoor temperatures). Such infants are at higher risk of hyperthermia or thermal stress.

Are there any safety concerns to consider when purchasing second-hand sleeping products?

Babies can suffocate during sleep due to unsafe cots and bassinettes. This occurs by wedging of the infant's face, neck or chest between sleeping surfaces and/or bedding. Unintentional suffocation is preventable, and can be minimised if the right precautions are taken when purchasing sleep products.

Where deaths have occurred, cots and bassinettes commonly had an inappropriately sized mattress that allowed for wedging between the mattress and the base of the cot. Another common factor was that the sides of the cot were faulty and allowed infants to slip through and become trapped. 

This post, originally published on the Trade Me Trust & Safety blog, emphasises a number of guidelines for families and whanau when buying sleeping products. 

Is gastro-esophageal (GE) reflux, also known as ‘spilling’, a risk for SIDS/SUDI?

GE reflux is unlikely to be related to SIDS/SUDI. 

Examinations of the tissues from the lungs of babies who have died of SIDS occasionally show gastric contents (that is, stomach fluids) within the airways. It is unclear if the gastric contents that come up with the GE reflux are then breathed in by the infant leading to suffocation and death, or if GE reflux is an event that occurs during the process of dying.

Some researchers have suggested that GE reflux occurs after death, as a consequence of cardiopulmonary resuscitation (CPR), where the pressure from the CPR causes gastric contents to enter the lung.

Breathing in gastric contents can lead to death in infants who have impaired coughing or auto-resuscitative mechanisms. In most healthy infants, however, aspiration of gastric contents is trivial, will result in coughing to clear the airway and is very unlikely to cause death.

An alternative mechanism has been proposed by Page and Jeffery (2000)[13]. They suggest that death might occur in some infants by reflex apnoea, which is caused by gastric acids stimulating the laryngeal chemo-receptors during sleep. Breathing gastric acids into the upper airways, especially larynx, might cause this. This could be fatal when refluxed to the level of the pharynx during sleep. On its own, this is an infrequent event which is usually harmless, but it could be fatal in infants with impaired swallowing and depressed arousal (due to factors such as prone sleeping, prematurity, sedatives, seizures or upper respiratory tract infections).

There are some experimental studies supporting this idea, but there are also several epidemiological studies that do not support it. The New Zealand Cot Death Study estimated the likelihood of GE reflux by recording whether the deceased infant had ‘vomiting or spill more than 30 minutes after feeding’. The data (shown here) showed that GE reflux was just as frequent in infants that did not die (these were the controls) and was no higher in SIDS cases.

  Case Control OR (95% CI)
Last 2 weeks 28.2% 30.9% 0.88 (0.69-1.13%)
Last 2 days 17.2% 19.7% 0.85 (0.63-1.13)



  1.  Arnestad M, Andersen M, Rognum TO. 1997. Is the use of dummy or carry-cot of importance for sudden infant death? European Journal of Pediatrics 156(12): 968-70.
  2.  Some authorities include a motor vehicle crash that kills an infant within the SUDI definition, but the Child and Youth Mortality Review Committee (CYMRC) in New Zealand does not. The CYMRC believes that, although a death in a vehicle crash may certainly be sudden and the circumstances leading to the death are unexpected, the death itself is not unexpected due to the lethality of the injuries that are inflicted.
  3.  Krous HF, Beckwith JB, Byard RW, et al. Sudden infant death syndrome and unclassified sudden infant deaths: a definitional and diagnostic approach. Pediatrics. 2004. 114: 234–8.
  4.  Ministry of Health. 2013. Fetal and Infant Deaths 2010. Available at:
  5.  Spiers PS. Estimated rates of concordancy for the sudden infant death syndrome in twins. American Journal of Epidemiology, 1974:1001-7; Peterson DR, Chinn NM, Fisher LD. The sudden infant death syndrome: repetitions in families. Journal of Pediatrics, 1980. 97:263- 267.
  6.  Wilson, CA, Taylor BJ, Laing RM, Williams SM, Mitchell EA and the New Zealand Cot Death Study Group. 1994. Clothing and bedding and its relevance to sudden infant death syndrome: Further results from the New Zealand Cot Death Study. Journal of Paediatrics and Child Health 30(6): 506-512.
  7.  Tonkin SL, McIntosh CG, Hadden W, Dakin C, Rowley S, Gunn AJ. Simple car seat insert to prevent upper airway narrowing in preterm infants: a pilot study. Pediatrics 2003;112: 907–13)
  8.  Byard RW, Beal SM. 1997. V-shaped pillows and unsafe infant sleeping. J Paediatr Child Health 33: 171-3.
  9.  Mitchell EA, et al. 1995. Immunisation and the sudden infant death syndrome. Arch Dis Child 73:498-501).
  10.  Vennemann, et al. 2007. Sudden infant death syndrome: No increased risk after immunisation. Vaccine 25:336-40
  11.  Vennemann, et al. 2007. Do immunisations reduce the risk of SIDS? A meta-analysis. Vaccine 25:4875-9).
  12.  Cote A, et al. 2008. Sudden infant death in sitting devices. Arch Dis Child 93:384-9.
  13.  Page M, Jeffery H. 2000 The role of gastro-oesophageal reflux in the aetiology of SIDS. Early Human Development 59(2): 127-149.

Last updated 06/12/2017