Sudden infant death syndrome (SIDS)

Sudden infant death syndrome is the sudden death of an apparently healthy baby under one year old that remains unexplained after everything has been checked. It used to be called cot death. It is rare, and the chance of it happening to any particular family is low. But one thing is known for certain: a handful of simple sleeping conditions bring the risk down substantially, and they genuinely work — wherever parents have been told about them, these deaths have fallen several times over. That is what this whole page is about. It is written both for people expecting a baby and for people who have lost one; if you are reading it for the second reason, here is the essential point first: this was not your fault.

What is actually known

Nobody knows the exact cause, and the honest thing is to say so. The most widely accepted explanation describes three circumstances coming together. The first is the baby: in some infants the parts of the brain that govern breathing, heart rhythm and waking up mature a little more slowly, so the baby responds less well to a shortage of air and fails to wake where another baby would. The second is age: almost all cases fall within the first six months, most often between one and four months, and after the first birthday the term is no longer used. The third is something external during sleep: lying face down, soft bedding, a covered head, overheating, tobacco smoke.

The first two cannot be changed. The third can be changed entirely, which is why the conversation about safe sleep is worth having at all. The risk is somewhat higher in babies born early or with a low birth weight, and slightly higher in boys than in girls. This is not a sentence and not a reason to live in fear; it is a reason to take the sleeping arrangements more seriously.

On the back, in their own cot

Two measures account for most of the benefit, and both are simple.

• Put your baby on their back to sleep — at night, for daytime naps, and also when a grandparent or a childminder settles them. On the side is not a safe alternative: from there a baby rolls easily onto their front. Once a baby can turn over unaided in both directions, there is no need to spend the night rolling them back; simply keep starting them off on their back.
• A baby is best in their own cot but in the parents' room for the first few months, and if possible until six months. Close by, within arm's reach, but on their own surface. That combination, a separate cot in a shared room, lowers the risk appreciably.

The surface should be flat and firm: a solid mattress that fits the cot exactly, with no gaps at the edges, covered only by a well-tucked sheet. Anything soft, sagging or sloped is unsuitable. A sofa, an armchair, a soft adult bed, an air mattress, a sleep nest and a feeding pillow are not places to sleep.

In a car seat, a bouncer or a swing a baby's head can drop onto the chest and make breathing harder. If they fall asleep in one, move them onto a flat surface once you are home.

What belongs in the cot and what does not

An ideal cot looks empty, and that is not an exaggeration. Take out pillows, duvets and blankets, padded bumpers, soft toys, sleep positioners and anti-roll wedges, canopies, and anything with long ties or cords. All of it can end up over the face, and a baby cannot free themselves.

Instead of a blanket, a baby sleeping bag in the right size and weight is convenient. If you do use a thin blanket, tuck it under the mattress so it reaches no higher than the chest, with the baby's feet at the foot of the cot so they cannot slide down underneath it.

Do not let a baby get too warm. An infant needs roughly one more layer than an adult finds comfortable in the same room, and no more than that. A cool room beats a warm one: somewhere around 16 to 20 °C is the usual guide. A hat indoors is not needed for sleep, because babies lose surplus heat through the head. To judge whether a baby is too warm, feel the neck and the back between the shoulder blades rather than the hands and feet, which are always cool. Damp hair, a flushed face and fast breathing mean it is time to uncover and let some air in.

If you swaddle, keep it loose around the hips, always place the baby on their back, and stop swaddling as soon as they start trying to roll.

Sharing a bed: where the line falls

This needs to be said plainly and without lecturing. Plenty of parents fall asleep with their baby, particularly during night feeds, and pretending otherwise helps nobody; it is far more useful to know which situations are genuinely dangerous.

Never fall asleep with a baby on a sofa or in an armchair. This is the most dangerous situation of all: the baby slips into the gap between your body and the back of the seat, or ends up face down against soft upholstery. If you feel yourself drifting off, move the baby into the cot, even if the feed is unfinished and you hate to disturb them.

Do not take your baby into bed if you or your partner:

• smoke, wherever the smoking happens;
• have been drinking alcohol;
• have taken sleeping tablets, sedatives or other medicines that cause drowsiness, or any recreational drugs;
• are extremely exhausted and sleeping more heavily than usual;
• have a baby who was born early or with a low birth weight.

If your baby does end up sleeping beside you, clear pillows, duvets and everything else out of the space where they lie, never leave them alone on an adult bed, do not place them between two adults, and make sure they cannot fall out or become wedged against the wall. And do not let a baby sleep in a bed with older children.

What else brings the risk down

Stopping smoking is the single most powerful thing anyone can do. Smoking in pregnancy and tobacco smoke around a baby raise the risk markedly, and the less smoke there is the better; this applies to electronic cigarettes, to smoking on the balcony and to the smell left in clothing. If quitting does not work out, any reduction and a complete ban on smoking in the home and the car already help. A doctor can help with stopping, and there is nothing shameful about asking.

Breastfeeding lowers the risk, and more clearly the longer it continues. It needs one caveat, without which the sentence sounds unjust: this is not a reproach to anyone who could not do it. Breastfeeding does not work out for everyone, often for reasons that have nothing to do with the mother's choices. A formula-fed baby in a safe cot, on their back, in a smoke-free room is far better protected than a breastfed baby in unsafe sleeping conditions. The measures add up, and each one counts on its own.

Other things help too: immunisations kept up to date according to the national schedule, since vaccinated babies have a lower risk of SIDS, and avoiding alcohol in pregnancy. Some studies link a lower risk with offering a dummy at the start of sleep; if the baby refuses it or it falls out, there is no need to insist, and where breastfeeding is under way it is sensible to wait until feeding is well established.

Home breathing monitors: the honest answer

Parents are frequently offered devices that watch breathing, pulse or blood oxygen: mats under the mattress, socks, wristbands, clips on the nappy. The question is a fair one, and the answer is this: no home monitor has been shown to reduce the risk of SIDS. That holds for medical devices and for consumer gadgets with a phone app alike.

They also have a downside. False alarms wear the whole family out and cost everyone sleep, and the feeling of being protected sometimes displaces the things that actually work: parents relax and stop paying attention to how the baby is lying and what is in the cot. Whether to buy one is a personal decision and there is nothing wrong with it; the point is simply not to treat it as a substitute for safe sleep. Babies with medical conditions for whom a doctor has prescribed monitoring are a separate matter: there the device has a different job and different reasons behind it.

When a baby needs help urgently

Call an ambulance (112 is the single emergency number across Europe) if your baby:

• has stopped breathing, is breathing with pauses, or has turned blue or grey;
• is struggling to breathe: the spaces between the ribs and the hollow at the neck pull in, there is grunting, the nostrils flare;
• has gone floppy like a rag doll, or conversely is stiff and rigid;
• will not wake, does not respond to you, or stares fixedly at one point;
• has a fit for the first time, even if they seem to recover afterwards.

While the ambulance is on its way you will be talked through what to do, including how to give rescue breaths and chest compressions if it comes to that. A first aid course for parents is a very sensible use of a few hours: it is not about fear, it is about confidence.

A baby should be seen by a doctor the same day if they develop a temperature, refuse feeds, become noticeably lethargic or unusually irritable, wet fewer nappies than usual, develop a rash, start breathing faster, or if the cry has changed. Small babies are ill often and it is almost always trivial, but the first months have one particular feature: deterioration can be quick, and "something does not seem right with him" is a legitimate reason to seek advice even when you cannot put it into words.

If your baby has died

After the sudden death of a baby there is always an investigation and a post-mortem examination. It is hard, and it is often experienced as suspicion, but at bottom it is a required procedure: it exists to establish what happened, and in most cases it is precisely what lifts a non-existent blame off the parents. Conversations with doctors and with the police are part of that process, not a verdict on how you looked after your child.

This was not your fault. Thoughts along the lines of "I wasn't watching", "I went to sleep", "I should have checked once more" come to almost everyone and bear no relation to what actually happened. Grief for a child does not run to a timetable: it arrives in waves, returns months later, is lived differently by a mother and a father, and reaches older siblings and grandparents too. Help can be sought at any point — a week later, a year later, ten years later — and there is no need to wait until things become unbearable. Talking to a psychologist who works with bereavement helps, so do groups of parents who have been through the same thing, and so does a doctor who will simply answer the questions that have piled up. One more thing: if a subsequent pregnancy brings fear with it, say so out loud to a professional early, because that is something people work with.

Online consultation

An emergency is handled by calling an ambulance, not by messaging a doctor. But most questions about safe sleep are not emergencies, and they are well suited to a remote appointment. Online you can go calmly through how sleep is organised for your particular baby: what to do about night feeds, how to handle a baby who flatly refuses to sleep on their back, whether your cot and mattress are suitable, how to dress a baby at night in hot weather. A doctor can help make sense of the posseting and the breathing pauses you have noticed, and say whether a particular symptom needs attention today or can wait until morning. Stopping smoking before the birth and getting feeding established are also good subjects for a remote appointment. And for parents who have lost a baby, a conversation at a distance is sometimes easier to face than one in person; that too is possible, including a long time afterwards.

This material is for information only and does not replace medical advice.