What is Sudden Infant Death?

Thirty-one years ago, tragically, the broadcaster and TV presenter Anne Diamond lost her four-month-old baby son Sebastian to cot death. At that time, little was understood about cot death, which was costing thousands of babies’ lives in the 1970s and 1980s. It became an epidemic between 1970 and 1991, and, at its peak, babies in some of the world’s richest countries were dying at the rate of one in every 250 live births each year. In 1989 in the UK, there were 1,545 cot death cases.

The death of Anne Diamond’s baby had happened to coincide with research on the phenomenon being published for the first time in the Netherlands, New Zealand and the UK by Professor Peter Fleming, of the University of Bristol and University Hospital Bristol. In spite of her grief at the bereavement, she used her devastating experience to spearhead the UK’s Back to Sleep Campaign (part of a worldwide Back to Sleep Campaign), having raised funding for advertising, and enlisting parenting charity the National Childbirth Trust (NCT). She also lobbied then Health Secretary Virginia Bottomley into accepting the need for a strong public health message about the risks associated with Sudden Infant Death Syndrome (SIDS).

The year after the Back to Sleep campaign launched in the UK in 1991, SIDS cases in the UK fell to 647 in 1992.

Now, cot death is more widely known as Sudden Infant Death Syndrome, referred to more commonly as SIDS. Sudden infant death syndrome (SIDS) is always a tragedy, but it is no longer commonplace. NHS figures report that around 200 babies in the UK die suddenly and unexpectedly every year. This statistic may still sound alarming, but SIDS is now fairly rare and the risk of a baby dying from it is very low.

An Office for National Statistics (ONS) report states that:

• There were 170 unexplained infant deaths accounting for 7.1% of all infant deaths in England and Wales in 2019.
• In 2019, sudden infant deaths accounted for 59.4% of unexplained deaths.
• The unexplained infant mortality rate had been decreasing since records began in 2004 but has levelled out since 2014 and was 0.27 deaths per 1,000 live births in 2019.

What is sudden infant death syndrome?

Sudden infant death syndrome (SIDS), formerly known as cot death, is the sudden, unexpected and unexplained death of an apparently healthy baby, occurring in babies usually under a year old. The reason that SIDS was previously referred to as cot death was that many SIDS babies die when they are sleeping, although it can occasionally happen while they are awake. Research subsequently proved that the cot in itself was not a contributing factor for SIDS, hence the change in the term.

The majority (90%) of SIDS deaths occur before a baby reaches 6 months of age, and the number of SIDS deaths peaks between 1 month and 4 months of age. However, SIDS deaths can occur anytime during a baby’s first year.

The death of a baby younger than one year old that cannot be explained, even after a full investigation which includes a complete post-mortem, examination of the death scene and review of the clinical history, will usually be categorised as a SIDS death.

What are the signs and symptoms of sudden infant death syndrome?

Unfortunately, SIDS has no symptoms or warning signs. Babies who die of SIDS appear to be healthy before being put to bed. They show no signs of struggle, and are often found in the same position as when they were placed in their bed. SIDS is named the cause of death only when no other cause is found.

If you are worried about your baby at any point, you can contact your midwife, health visitor or GP, or call NHS 111 for advice. However, Dial 999 for an ambulance if your baby:

• Stops breathing or turns blue.
• Is struggling for breath.
• Is unconscious or seems unaware of what’s going on.
• Will not wake up.
• Has a fit for the first time, even if they seem to recover.

What physical factors cause sudden infant death syndrome?

In the late 1970s following a wave of SIDS deaths, some people suspected that the deaths were related to the diphtheria-tetanus toxoids-pertussis vaccine. However, subsequent studies noted that there is no relationship between SIDS and any vaccines.

It is still unclear at this time exactly what causes SIDS and research is ongoing to find the cause or causes of SIDS. The ONS report, mentioned above, collated data on SIDS deaths which revealed that:

• Unexplained infant deaths are more likely to occur in males during the post-neonatal period, that is babies aged between 28 days and 1 year. In 2004, males had 0.58 unexplained deaths per 1,000 live births compared with 0.41 for females. In 2019, males had 0.29 unexplained deaths per 1,000 live births compared with 0.24 for females.
• Unexplained infant deaths are more likely to occur in low birthweight babies. Since 2004, the rate of unexplained infant deaths has been around four times higher among low birthweight babies, that is less than 2,500g, than babies with a normal birthweight, that is 2,500g and over.
• Maternal age is a risk factor for infant mortality generally and this holds true for unexplained deaths. In 2019, mothers aged under 20 were over five times more likely to experience unexplained infant deaths than mothers aged over 40.
• The unexplained infant mortality rate for babies of mothers born in the UK is more than double the rate for babies of mothers born outside of the UK.

Researchers have looked at many factors including whether SIDS runs in families; however, at this time there has been no direct link proven between SIDS and a genetic predisposition.

A very recent study by Dr Carmel Harrington and a team of scientists at the University of Sydney, found babies who died of sudden infant death syndrome (SIDS) had lower levels of an enzyme that helps humans rouse from sleep. Researchers behind the finding suggest the lower levels of the enzyme represent a dysfunction of the nervous system, and therefore an inherent vulnerability of the SIDS infants. They concluded that this finding represented the possibility for the identification of infants at risk of SIDS prior to death and that it opens new avenues for future research into specific interventions. The findings were published in 2022 in the UK medical journal, The Lancet’s eBioMedicine.

What environmental factors cause sudden infant death syndrome?

Some experts believe SIDS occurs at a particular stage in a baby’s development and that it affects babies vulnerable to certain environmental stresses such as:

• Tobacco smoke.
• Getting tangled in bedding.
• Getting too hot during sleep.
• A minor illness or a breathing obstruction.
• Co-sleeping, that is sleeping with a baby on a bed, sofa or chair.
• Tummy sleeping.*

Babies who die of SIDS are thought to have problems in the way they respond to these stresses and how they regulate their heart rate, breathing and temperature.

*In the mid-1980s Peter Fleming, Professor of Infant Health and Developmental Physiology, was just starting the Avon Cot Death Study when he read a Dutch report which suggested that putting babies to sleep on their fronts led to a high risk of cot death. Fleming immediately analysed the Avon data and found that indeed, 93 per cent of the babies who had died had been put to sleep lying on their fronts.

What are the risk factors of sudden infant death syndrome?

Although a number of SIDS risk factors are suspected, these have not been studied extensively enough to draw any firm conclusion. For example, studies have identified poor bedroom ventilation as a potential risk factor for SIDS, but more research is needed regarding this topic. Other potential risk factors that might make a baby more vulnerable to SIDS have been previously referred to in this article as areas that researchers are studying as potential causes of SIDS.

The predominant risk factor, however, as identified by Peter Fleming et al, is tummy or front sleeping. That is not to say that babies do not need time on their tummies, but this should only be when they are supervised, fully awake, and for only short periods of time, around 3–5 minutes.

The time that a baby spends on their tummy is not only an important way to prevent flat spots on a baby’s head, but it is also an important part of a baby’s normal growth, as it makes neck and shoulder muscles stronger and improves motor skills so that a baby can start to sit up, crawl, walk and complete an action.

However, when sleeping, the safest place for a baby to sleep is in a cot by the parents’ bedside and placed on their back. This is just as important for daytime naps too. A study found that the babies who died during the day were more likely to have been placed on their side than on their back for their daytime naps, they were more likely to be found with their heads covered by the bedclothes than the babies who didn’t die, and, in particular, 75 per cent of the babies who died in the daytime were sleeping in a room where there was no adult present.

How to reduce the risk of sudden infant death syndrome?

You should keep in mind that SIDS is very rare; however, taking the following precautions to reduce any risks may help to prevent the possibility of SIDS:

• The most effective method of reducing the risk of SIDS is putting a baby under one year of age on their back to sleep. Babies who are placed on their tummies or sides to sleep may have more difficulty breathing than those placed on their backs.
• Place your baby in the feet-to-foot position, that is with their feet touching the end of the cot.
• Keep your baby’s head uncovered – their bedding should be tucked in no higher than their shoulders.
• Use a mattress that is firm, flat, waterproof and in good condition.
• Keep the room at a temperature that is comfortable, about 16°C to 20°C is ideal.
• Babies should never sleep with a hot water bottle or electric blanket, next to a radiator, heater or fire, or in direct sunshine.
• Avoid sleeping on a sofa or in an armchair with your baby. Studies have found that sharing an armchair or a sofa together with your baby whilst you both sleep, may increase the risks of SIDS.
• Prevent your baby from overheating. Being too warm while sleeping can increase the risk of SIDS.
• Don’t share a bed with your baby. Sleeping in the same bed as the parents, siblings or pets increases the risk of SIDS, because of the potential for blocking the baby’s airways.
• Do not smoke or let anyone smoke in the same room as your baby, both before and after birth.
• If carrying your baby in a sling or carrier, do not cover their head with the sling material or with a muslin.

The American Academy of Paediatrics (AAP) have published guidance and recommendations for reducing infant deaths in the sleep environment in 2016 and have since updated this in 2022.

Final thoughts

A SIDS death is a tragedy that prompts intense emotional reactions among surviving family members, parents and particularly any siblings. If you or someone you know has lost a baby to SIDS and you want to talk to someone in confidence, there are a number of helplines you can contact:

• Sands supports anyone affected by the death of a baby, telephone: 0808 164 3332 helpline@sands.org.uk.
• A Child of Mine Help for Bereaved Parents. Helpline on 07803 751229 from 9:00am – 5:00pm. Telephone: 01785 283 434. Email: hello@achildofmine.org.uk.
• Care for the Family provides parent support, family support and bereavement support. Telephone: 029 2081 0800. Email: mail@cff.org.uk.
• Child Bereavement UK National Helpline: 0800 02 888 40 Monday to Friday, from 9:00am – 5:0pm. Email: support@childbereavementuk.org.
• Petals Baby Loss Counselling Charity. Telephone (counselling queries): 0300 688 0068 (local charges apply). Email: counselling@petalscharity.org.
• The Child Death Helpline offers support to anyone affected by the death of a child of any age, under any circumstances, however recent or long ago. Helpline: Freephone 0800 282 986 or 0808 800 6019 Monday to Friday 10am to 1pm, Tuesdays 1pm to 4pm, Wednesdays 1pm to 4pm, Evenings 7pm to 10pm. Email: contact@childdeathhelpline.org.
• National Childbirth Trust support line 0300 330 0700.
• The Scottish Cot Death Trust, telephone 0141 357 3946 for information or support. Email: contact@scottishcotdeathtrust.org.