Sudden unexpected infant death (SUID) is the sudden, unexpected death of an infant under 1 year. It includes:

• Sudden infant death syndrome (SIDS) — death of an infant under 1 year, usually during sleep, that remains unexplained after a complete investigation (autopsy, death-scene investigation, and review of the clinical history)
• Accidental suffocation and strangulation in bed — soft bedding, overlay by an adult, entrapment between mattress and wall, strangulation
• Deaths of undetermined cause

In the US, about 3,500 infants die suddenly and unexpectedly during sleep each year. SIDS is a diagnosis of exclusion; the cause of death can be established only after investigation.

Triple-risk model: SIDS occurs when three factors coincide:

1. A vulnerable infant — e.g., abnormal brainstem control of breathing and arousal, prematurity, prenatal smoke exposure
2. A critical developmental period — peak at 1–4 months; about 90% of SIDS deaths occur before 6 months
3. An outside stressor — prone or side sleeping, soft bedding, face covering, overheating, bed-sharing, smoke exposure

A normal infant rebreathing expired air or becoming hypoxic will arouse and turn the head; a vulnerable infant may fail to arouse.

Risk factors

Protective factors: supine sleep for every sleep, breastfeeding or human milk, room-sharing without bed-sharing, pacifier at sleep, up-to-date immunizations, prenatal care, and a smoke-free environment.

Brief resolved unexplained event (BRUE): a brief (usually under 1 minute) episode in an infant of color change, breathing change, tone change, or altered responsiveness that has resolved and has no explanation after assessment. BRUE replaced the older term "apparent life-threatening event"; it is not considered a precursor of SIDS, but it needs evaluation.

• SIDS is determined after death: autopsy, death-scene investigation (sleep position, surface, bedding, temperature, other people present), review of history, and toxicology
• No test predicts SIDS in a living infant
• Home cardiorespiratory (apnea) monitors are not recommended as a strategy to reduce SIDS; consumer "wearable" monitors marketed to parents have no proven benefit and should not replace safe-sleep practices. Monitors may still be ordered for other medical reasons (e.g., some preterm infants with apnea or infants with airway or oxygen needs)

There is no treatment; management is prevention and family support after a death.

AAP 2022 safe sleep recommendations (summary)

• Back to sleep for every sleep — naps and night — until 1 year. Once an infant can roll both ways, they may stay in the position they choose, but are always placed on the back
• Firm, flat, level surface (incline no more than 10 degrees) with a fitted sheet only — crib, bassinet, or portable play yard meeting safety standards
• Nothing soft in the sleep area: no pillows, blankets, quilts, bumper pads, positioners, or stuffed toys
• Room-share without bed-sharing, ideally for at least the first 6 months — infant on a separate surface close to the parents' bed. The AAP does not recommend bed-sharing under any circumstances
• Never sleep with an infant on a sofa, couch, or armchair
• Human milk / breastfeeding reduces risk; bring the infant into bed to feed if needed but return them to their own surface; if a parent might fall asleep while feeding, feed on an adult bed cleared of pillows and blankets rather than a sofa, and return the infant as soon as the parent wakes
• Offer a pacifier at naps and bedtime; for breastfed infants, once breastfeeding is well established; do not reinsert once asleep, do not force, and never hang it around the neck or attach it to clothing
• Avoid smoke, nicotine, alcohol, and drugs during pregnancy and after birth
• Avoid overheating and head covering; dress the infant in no more than one layer more than an adult would wear; use a wearable blanket instead of loose blankets
• Swaddling: always on the back; stop when the infant shows signs of trying to roll (often around 3–4 months); no weighted swaddles, sleep sacks, or blankets
• Sitting devices (car seats, strollers, swings, infant carriers) are not for routine sleep; if the infant falls asleep in one, move them to a flat sleep surface as soon as practical
• Supervised, awake tummy time daily, starting soon after hospital discharge, increasing to at least 15–30 minutes total per day by 7 weeks — prevents positional plagiocephaly and supports motor development
• Immunize on schedule; do not use products claiming to reduce SIDS risk

Listed in priority order.

1. Model safe sleep in the hospital from the first sleep: healthy newborns supine in a bare bassinet; preterm infants in the NICU are transitioned to supine, flat, bare sleep well before discharge (by about 32 weeks' postmenstrual age when medically stable) so parents see the practice they will use at home
2. Assess each family's sleep plan: where will the infant sleep? Who else is in the bed? Smoking, alcohol, or drug use? Room temperature? Access to a crib or bassinet?
3. Teach and demonstrate the recommendations using simple messages — Alone, on the Back, in a Crib (or bassinet), in the parents' room; use teach-back
4. Respect culture while reducing risk: when a family plans to bed-share, explain the highest-risk situations (sofas, smoking, alcohol, sedating drugs, soft bedding, infants under 4 months, preterm infants) and provide safer alternatives (bedside bassinet, safe portable crib)
5. Promote breastfeeding and smoke-free homes (referral to cessation support)
6. Teach other caregivers — grandparents, babysitters, child care workers — who may follow older practices (prone sleep, blankets)
7. After a SIDS death, support the family
   • Provide a quiet, private place; allow parents to see, hold, and say goodbye to their infant
   • Use the infant's name; offer simple, honest information
   • Non-judgmental, empathic support — parents often feel intense guilt; avoid questions that sound like blame
   • Explain that an autopsy and death-scene investigation are standard for every sudden infant death and do not mean the parents are suspected
   • Offer mementos (handprints, footprints, lock of hair, photos) according to family wishes and culture
   • Refer to bereavement support and help with siblings' grief; address lactation suppression for a breastfeeding mother
   • Provide support for future pregnancies (smoking cessation, safe sleep reinforcement)

• Place the infant on the back for every sleep, including naps, by everyone who cares for the baby
• Use a firm, flat crib or bassinet with only a fitted sheet; keep it in the parents' room for at least 6 months
• Do not sleep with the infant on a sofa or armchair, especially when tired, after alcohol, or when anyone smokes
• Keep the room comfortable, not hot; do not cover the infant's head
• Offer a pacifier at sleep time; breastfeed as long as possible
• Tummy time only when awake and watched
• Do not rely on home monitors or products marketed to prevent SIDS
• Learn infant CPR

• Infant found unresponsive: shout for help and start infant CPR; call emergency services (use a phone on speaker while doing CPR; if alone without a phone, give about 2 minutes of CPR first, then call)
• Positional plagiocephaly or torticollis from lack of tummy time (not a reason to stop back sleeping)
• BRUE (pale or cyanotic spell, limpness, breathing pause) — needs same-day evaluation
• Unsafe sleep found on home visits (sofa sleeping, soft bedding, smoker bed-sharing) — immediate teaching and follow-up
• Family grief complicated by guilt, depression, or marital strain after an infant death — refer

• SIDS = unexplained death under 1 year after full investigation (autopsy, scene, history)
• Peak 1–4 months; most deaths before 6 months; male > female
• Biggest modifiable risks: prone or side sleeping, soft bedding, bed-sharing, smoke exposure, overheating
• Protective: supine sleep, breastfeeding, room-sharing, pacifier, immunizations
• Room-share without bed-sharing, ideally for the first 6 months
• Firm, flat surface (incline no more than 10°); no pillows, bumpers, blankets, or toys
• Sofas and armchairs are extremely dangerous for sleeping with an infant
• Stop swaddling at signs of rolling; no weighted products
• Home apnea monitors do not prevent SIDS
• Maternal smoking cessation is protective; continuing to smoke is a risk
• After a death: non-judgmental emotional support first; autopsy is routine, not an accusation