What is SUDI?

When a healthy baby dies suddenly and unexpectedly and there is no apparent reason at the outset why they died, the term SUDI is used. This stands for Sudden Unexpected Death in Infancy. While SUDI is most common for infants under 6 months of age, it can occur in children aged between 6-12 months and also in children older than 12 months and the term sudden unexpected death in childhood (SUDC) is then used.

In the past, cot death was used as a general term and a medical cause of death. SIDS (Sudden Infant Death Syndrome) is also used around the world.

Infants may be discovered in their own cot or crib, sharing a sleep space such as an adult bed, sofa or chair, in their pram, car seat or infant carrier. SUDI can sometimes although rarely be witnessed to happen when an infant is sleeping in someone’s arms. SUDIs can occur during any sleep period not just a night time sleep. The majority are not witnessed. The baby or young child is discovered by a parent or care giver when they waken or go to check on them. There is no sign of a struggle, or of any distress.

SUDI by definition are deaths which are not expected, however, we have a growing knowledge of risk factors associated with these deaths. Research continues to help us understand more about SUDI. Despite being very rare, SUDI is the most common cause of death for infants between 1 and 12 months old. In Scotland, a healthy baby or young child dies suddenly and unexpectedly every 9 days.

In Scotland when a death is sudden and unexpected, it must by law be reported to the Procurators Fiscal and investigated by the police acting on behalf of the Procurators Fiscal. A post-mortem examination will be instructed to try to find out the cause of the child’s death.

In some cases, a cause of death is identified at the initial post-mortem examination. In some cases, a cause of death may be identified after results from ancillary tests performed as part of the full post-mortem become available. These ancillary tests results can take many months. In many SUDI cases no cause of death will be found and the death will remain unexplained.

In every SUDI and SUD there will be an investigation to ascertain why the child died. This includes a post-mortem and a full investigation into the circumstances of the child’s death. This is required by law and does not imply suspicion of anything unlawful. Each year in the Scotland there are a very small number of infant and child deaths which are discovered to have been caused by a non-accidental injury (NAI).

Can SUDI  be avoided?

SUDI is very rare, but all babies are potentially at risk. In Scotland each year there is an average of 53,000 live births and around 40 SUDI. Our aim is to eradicate SUDI because every baby and young child’s life matters. We want all sleep related deaths in babies to be a thing of the past. We want the pain and suffering that families experience when their child dies suddenly and unexpectedly to stop.

In general, SUDI rates have reduced significantly since the early 1990’s which was mainly attributed to the successful – Back to Sleep campaign. Given the rate of SUDI within the infant population are the messages that important? The simple answer is, YES! If 40 adults or teenagers died each year and it was known that many of the deaths could be prevented nobody would accept that the deaths were ‘just something that happen’.

SUDI-breakdownIt is not a comfortable topic but the truth is that most SUDI occur with more than one risk factor. Very few deaths occur in Scotland where there are no risk factors present. We need science to help us understand these deaths more if we are to prevent them. For the remaining deaths where we know things could have been changed or modified. We rely on parents, caregivers and those professionals working with families to know about risks and to make their decisions based on knowing all of the facts and understanding what they can do to make a difference to their baby’s sleep times.

Any factor which makes a baby less vulnerable when they are born (reducing risks as the baby is developing during pregnancy, such as smoking cessation before conception or during early pregnancy), reducing risks after the baby is born and ensuring each sleep time is a safe one each play a part in reducing risks of SUDI

We believe that if every baby slept in the safest way possible, we would reduce these tragic deaths by at least 50 %. In addition, some modifiable risk factors may add stress to babies and young children who are known to have died from infections, so risks can perhaps be reduced for other deaths.

When does SUDI occur?

Researchers around the world understand that SUDI most often happens when modifiable risk factors are present during a critical developmental period in an infant who has an immature or dysfunctional cardiorespiratory and/ or arousal system. This means that when the baby has to Triple-risk-model-for-unexplained-SUDIdeal with something which challenges the normal response to breathing, they are less able to respond in a way that protects them.

What makes a baby more vulnerable is not entirely clear. Why do some babies have a more immature cardiorespiratory and/ or arousal protective response?

Key messages:

Babies and young children are reliant on their caregivers to make decisions which keep them safe. This is not challenged for other infant care practices such as laws in Scotland which protect babies and children when they are travelling in vehicles.  A baby is reliant on their care givers to keep them safe during sleep times.

Across the country many infants sleep in environments and in circumstances which are not safest for them. The majority do not die. Risk factors are another way of saying there is a chance of something happening. It does not mean it will or it won’t. Our role as an organisation is to ensure there is an awareness of risk factors and an understanding of why babies need to sleep safely. Parents and care givers make all sorts of decisions every day about how they care for their baby. Most will not have a potential to cause harm or death.

It is unacceptable that parents find out after their child died that there were risk factors that they were unaware of. We are not responsible for decision that parents and caregivers make but we and many other agencies are responsible for providing information so that they can make informed choices.

Our education sessions discuss the evidence behind known risk factors, the interplay between such factors and how risks can be reduced as much as possible.

Defeating SUDI is a battle on two fronts – funding research to identify causes and build greater understanding of why it occurs, and by educating and promoting ways to reduce the factors that create increased risk

SUDI is sadly not always preventable, because in a small number of cases we know there are no risk factors and nothing could be done to reduce risk further. However, following the safety guidelines can reduce the risk of it occurring, especially when it may be the case that an infant has died and thier sleep environment has been identified as a factor.

In Scotland most SUDI are caused when there is a combination of a vulnerable infant and a sleep environment with factors which could reduce the infant’s ability to breathe properly.

This extends from a very vulnerable baby sleeping in the safest way possible to a normal baby sleeping in a very hazardous environment.

If we are to reduce SUDI we must address factors across this spectrum.

  • Only medical research can address the vulnerable baby who is sleeping in the safest way possible. These account for a small number of SUDI in Scotland and are thought to be genetic anomalies, developmental anomalies as well as prematurity in the absence of modifiable pregnancy risk factors.
  • Ensure all baby’s are sleeping in a safe environment – on their back, in their own sleep space free from loose bedding, pillows and toys.
  • Ensure that the environment is one that is optimal for baby’s arousal – not too warm, correct clothing and bedding layer, no hat for sleeping, no tummy or side sleeping.
  • Ensure that the parents or caregivers are alert to baby’s needs. Not overly tired, no alcohol, drugs, should be in the same room for all sleep times day and night.

The following shows some brief key messages. For more detailed information visit our section on safe sleep messages.

SUDI factors we cannot affect.

These are factors inherent within a baby that cannot be changed or modified.

  • Vulnerable infants – an underlying condition that has hasn’t been identified
  • Critical development – viewed to be 2-4 months (although broadly seen as first 6 months). A key developmental/maturation period for babies as there is no exact time that development takes place and all babies grow and mature at different rates.
  • Time of year – 60% happen in winter or spring – this could be due to increased chance of infection, or overcompensating with too many blankets due to the cold weather.
  • Pre-term or low birth weight (< 2.5kg or 5.5 lbs) – although in some cases prematurity and low birth weight may be linked to modifiable risk factors.
  • Gender – boys are at increased risk. The exact reason is unclear but it is well understood that certain aspects of infant male developmental/maturation period is later than in female infants, such as regulatory centres which control homeostasis (regulation of bod breathing, temperature and blood pressure).
  • Twins & Multiples – these babies are more likely to be premature and/or low birth weight

Before exploring each modifiable factor in turn, it is worth looking at what basic factors can affect a baby’s breathing during sleep and why this is so.

Baby’s only breathe through their nose when they are very young. They do not breath through their mouths.

They have very small air passages and weak neck and jaw muscles.

Babies have large, heavy heads with a pronounced bulge at the back. They have short necks and short tongues.


This is the normal anatomy of a young baby’s head, neck and throat.baby's head

Note the baby’s features:

  • A large head
  • A rounded head at the back
  • The loose lower jaw
  • A short neck
  • A big tongue
  • In addition to this a young baby only breathes through their nostrils, which are very small and are easily compressed.

Because of their anatomy, a young baby can get into positions and situations which can affect their breathing. Very simply, anything which covers their face, or even their small nostrils can reduce the amount of air they breathe.

This can be something soft such as bedding, pillows, sleep positioners or toys in the space a baby is sleeping. Another person or pet in baby’s sleep environment could mean baby rolls against them or they could roll onto or against baby.

Anything that could squeeze the nostrils together, reducing the amount of air that can be breathed can be hazardous. Again, this includes anything in a baby’s sleep space that they can move against or which can move into their sleep space.

If a baby is sleeping in a semi-reclined or upright position, their heavy head can roll forwards. This creates a ‘chin -tucked-down’ position. In this position a baby’s small airways can become folded over which reduced the air they can breathe.

Because baby’s airways are so small, any pressure on their chest could reduce how effectively they can breathe. The weight of an adult’s or an older sibling’s arm laying over their chest or a pet lying on their chest could impede a baby taking deep enough breaths to take in enough oxygen.

Each of the situations described are some of the mechanisms by which a baby could die from asphyxia (through lack of oxygen) or by accidental suffocation.

The following factors  can be modified and affect a how vulnerable a baby is to SUDI, a baby’s sleep environment or their care givers ability to make the safest choices for baby’s sleep time:

  • Position
  • Surface
  • Bedding
  • Pillows
  • Space around baby
  • Room sharing
  • Temperature
  • Dummy use
  • Swaddling
  • Sharing a sleep space ( bed-sharing and sofa sharing)
  • Products that are sometimes used for baby’s sleep time such as car seats, bouncy chairs, swings, nests etc).
  • Smoking (prenatal and environment and consideration made for 2nd and 3rd hand smoke)
  • Alcohol consumption (recreational and habitual) prenatal and environment
  • Drug use (prescribed and illicit/ recreational and habitual) prenatal and environment