What is sudden infant death syndrome (SIDS)?

SIDS stands for sudden infant death syndrome, which is the name for what happens when a baby dies for no clear reason (Creery and Mikrogianakis 2006, Hauck and Tanabe 2009). There are around 300 cases of SIDS each year in the UK (FSID 2011b, Hauck and Tanabe 2009). It's most likely to happen during the first three months of a baby's life (FSID 2011b). We don’t really know what causes SIDS to happen (Hauck and Tanabe 2009), but we do know that certain factors can increase the risk.

Read on to learn more about SIDS, including how to protect your baby from risk factors associated with SIDS.

What is SIDS?

Sudden infant death syndrome (SIDS) is a diagnosis that's made when an apparently healthy baby dies unexpectedly, and for no clear reason (NHS 2015a, The Lullaby Trust 2015).

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SIDS used to be more commonly known as cot death. However, this term gave the misleading impression that babies were only affected when sleeping in a cot (The Lullaby Trust 2013a). SIDS may affect babies wherever they sleep.

How common is SIDS?

Fortunately, SIDS is rare. However, sadly, there are still just under 300 unexplained infant deaths every year in the UK (NHS 2015a, The Lullaby Trust 2015). About two thirds of these unexplained deaths are recorded as SIDS (ONS 2015, The Lullaby Trust 2015).

Why does SIDS happen?

No one knows for certain why some babies die in this way (NHS 2015a). It may be a combination of factors that affect some babies at a vulnerable stage in their development (Kinney et al 2009, NHS 2015a).

Experts think that some babies may have a problem with the part of the brain that controls breathing, heart rate and waking. When these babies experience stresses, such as getting too hot, or if their mouth or nose is covered by bedclothes, they are unable to regulate their heart rate, breathing and temperature, as other babies would (Kinney et al 2009).

Although there is no one infection that is known to cause SIDS, it's possible that the way some babies respond to slight infections, increases their risk of SIDS (Blackwell et al 2015, Ferrante and Opdal 2015, The Lullaby Trust 2013c).

When does SIDS happen?

SIDS most often occurs when a baby is thought to be sleeping (NHS 2015a). This is most likely to be at night, but it could happen at any time of the day, such as during a daytime nap (Blair et al 2006). It could happen in a cot, a pram, or even in their parent's arms (BMJ 2015).

SIDS is more common in winter, and tends to increase in particularly cold months (ONS 2015). This could be because infections increase at this time of the year (Alfelali 2014). It could also be because parents use extra bedclothes or put the heating on at night when it's very cold outside (ONS 2015). Find out how to keep your baby warm in cold weather, without overheating.

Which babies are most at risk?

Most cases of SIDS happen in the first six months (NHS 2015a), peaking at the age of two months to three months (The Lullaby Trust 2013c). The risk falls as your baby grows older, and relatively few deaths from SIDS occur after a year (The Lullaby Trust 2015).

The rate of SIDS is highest for babies of mums who are under 20 years when they have their baby (ONS 2015). This is likely to be due to lifestyle and living circumstances rather than age alone (The Lullaby Trust 2011). So knowing about safer sleep advice is particularly important if you're a young mum.

There are other factors that tend to increase the risk of SIDS, that are impossible to change or influence. For example, we know that SIDS occurs more often in boys than girls. This may be because of differences in hormones and how boys’ brains respond in comparison with girls.

The increase of SIDS is also higher if your baby was born prematurely (before 37 weeks) or had a low birth weight of less than 2.5kg (5.5lb) (Kinney et al 2009, ONS 2015, NHS 2015a, The Lullaby Trust 2013c). Although it’s natural to worry more if your baby is premature or has a low birth weight, remember that SIDS is rare. Most babies pass through the first six months of life without any problems.

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Find more advice and information on reducing the risk of SIDS.

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Sources

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