Sudden Unexpected Death in Infancy (SUDI - also known as SIDS or Cot Death)


Many parents would take any precaution to guarantee against their baby dying unexpectedly.

Sudden Unexpected Death in Infancy (SUDI) is extremely rare for babies if the advice below is followed:

In every place, for every sleep, check that baby is safe:

  • Face up
  • Face clear
  • Smokefree.

Baby should never be placed to sleep on their side or tummy. For further details go to the Ministry of Health website.

There has been a lot of discussion around SUDI over the years.  Parents Centre believes that it can best serve the needs of members by informing them of factors that are scientifically proven to reduce the risks to infants.

This is not to discredit or ignore alternative theories, but rather to recognise that however deeply felt, they require scientific validation to become fact.

There are no simple answers. It is up to parents to read widely around the topic and make their own decisions about what is best for their babies. Parents will make decisions on the basis of common sense, needs and tradition as well as science.


It is useful to know the background to the cot death debate in New Zealand.

In 1980, the cot death rate was 4 per 1000 live births. No one could offer any plausible explanation for why apparently healthy babies died.

During 1987-90, the Cot Death Study was carried out in New Zealand. This study was a scientific nation-wide study covering districts in New Zealand in which 78% of all births occurred. While the study did not identify a cause for cot death, it did identify four risk factors which could be modified to result in the deaths of fewer babies.

  • Sleep your baby on its back

  • Have a smokefree pregnancy and a smokefree home

  • If you smoke, or smoked during pregnancy, sleep your baby in its own bed

  • Breastfeed your baby

The National Cot Death Prevention Campaign that informed parents about the above four factors has seen the rate of cot death decline to 2 per 1000 live births.

Various possible causes of cot death have been proposed by scientists involved in the Cot Death Study. These include causes related to rebreathing, airway obstruction, mobility and overheating. All these causes remain unproven.

There is a further school of thought that cot death is caused by the baby being poisoned by any one of, or combination of, the gases stibine, phosphine and arsine.

These ideas are based on the belief that the chemicals from which these gases derive, antimony, phosphorus and arsenic, are naturally occurring substances and are found in cot mattresses (both covers and inners), bedding, sheepskins, PVC cot sheets, etc. In the presence of the very commonly occurring fungus scopulariopsis brevicaulis, these chemicals are converted into the above toxic gases which, as they are denser than air, remain in the baby's environment and poison him or her.

Advocates of this approach believe that the longer the baby's mattress is used, the greater the build-up of the fungus. This would explain the statistics that show cot death rarely occurs in a baby under one month and that the rate of cot death rises amongst older babies.

In 1997, the Ministry of Health called a meeting of cot death researchers and child health experts in a bid to resolve the conflicting messages that parents were receiving about cot death. The recommendation from the Ministry from that meeting was that currently available evidence does not support mattress wrapping as a preventive strategy for cot death.

Following the Ministry of Health meeting, the UK Expert Group to Investigate Cot Death Theories, released its final report. Among the conclusions of the UK Expert Group are the following:

  • There is no evidence that cot death is due to poisoning by phosphine, arsine and stibine
  • Overall, the toxic gas theory is unsubstantiated. There is no evidence to suggest that antimony and phosphorus-containing compounds used as fire retardants in PVC and other cot mattress materials are a cause of cot death.
  • The Ministry of Health issued a statement following the release of the final report of the UK Expert Group which said, "The British report definitively disproved the [toxic gas] theory" the Expert Group report has reached a comprehensive and scientifically valid conclusion that should put a lot of parents' minds at rest and clear up confusion around the issue."

Other Approaches

There are two further possible cot death prevention strategies that have been proposed. One of these is based on further analysis of existing data that shows the use of pacifiers or dummies appears to give some protection.

We know that the use of pacifiers, particularly with new babies, can reduce the need of babies to suckle and also lead to incorrect suckling techniques, thus preventing the successful establishment of breastfeeding. This needs to be taken into account and the use of pacifiers avoided for new-born babies, a time when the risk of cot death is in any case extremely low.

The latest possible cause of cot death to emerge is caffeine consumption in pregnancy. A Christchurch study claims that high levels of caffeine in pregnancy may have a stimulant effect on the baby's respiratory system and lead to a withdrawal effect after birth. According to this theory, breathing would stop without the stimulus caffeine provides. Whether or not cutting caffeine consumption during pregnancy joins the list of preventive factors remains to be seen.

As caffeine interferes with the way the body uses various vitamins and minerals and can lead to deficiencies, reduced caffeine intake during pregnancy is sound advice in any case.


As already stated, parents will need to decide for themselves what strategies they adopt for their babies.

Parents Centre advises parents to:

  • Keep an open mind on the range of theories about the causes of cot death

  • Be guided by existing evidence-based research

  • Be very aware of the modifiable factors that have come out of the Cot Death Study, i.e.
    - Sleep your baby on its back
    - Have a smokefree pregnancy and a smokefree home
    - If you smoke, or smoked during pregnancy, sleep your baby in its own bed
    - Breastfeed your baby.