Sudden Infant Defeat (SID) or Sudden Unexplained Infant Death (SUID) is the unexplained infant death in a child under one year old.

  • Majority of deaths are in the first four months (up to 90%1)
  • Room sharing can decrease the risk of SIDS under the theory that parents will be more attentive
    • Consider moving the child to own room for their sleep continuity and sleep training purposes after four months1

SIDs is correlated with:

  • sleeping on the stomach, possibly because babies sleep more deeply on stomach
  • Parental smoking and drinking
  • co-sleeping (still a factor after controlling for more major factors like smoking and drinking1)
  • Sharing a sofa with parent


Oster, E. Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. (Penguin Books, 2020).