Does SIDS Happen in the Daytime?

Does SIDS only occur at night? Why should I room-share at night but am fine to leave the room while they’re napping during the day?
—Naptime Hovering Mom

SIDS does not only occur at night. In one of the larger studies of the circumstances of SIDS cases, in the U.K., 83% of SIDS deaths occurred at night. This is the majority, but adjusting for the difference in typical sleep hours, it isn’t as disproportionate as it seems. The authors of the paper point out that they observe SIDS deaths at all hours of the day. Other studies have shown this as well, and suggest that stomach sleeping may be a particular risk factor during the day. The advice about putting infants to sleep on their back is, therefore, crucial for both day and night sleep.

The advice on room sharing is among the weakest-supported for SIDS prevention. The evidence to support it is based entirely on case-control studies, which are difficult to learn from (there is more on this in Cribsheet). I mention this only because the initial premise of this question is that room sharing is important at night, and I’m less convinced that is true.

To the extent that we think there might be some small impact of room sharing, there is no reason to think it would differ by time of day. I think the reason that we aren’t told to room-share during naps is that there is an implicit assumption that you’re around and paying more attention during naps. The main reason room sharing would be important during nighttime is that parents might be more aware of their baby while sleeping in that case. If you’re awake, perhaps you are already able to be aware.

This logic is a little tortured — presumably many of us leave our babies on their own to sleep during naps while we try to, say, cook dinner or wash dishes or doom-scroll. But I think that is what must be behind this idea.

My primary takeaway here is that it’s very important to adhere to the more important safe sleep tenets — back sleeping; no sleeping on chairs or sofas — both at night and during naps.