Swaddling increases quiet sleep duration and reduces the number of sleep state changes among infants naive to intervention1. Additionally the results indicate a reduction in crying. Swaddling should be done in a way that allows the baby to move their legs around2.
Swaddling and SIDS
Emily Oster concludes that swaddling does not increase the risk of SIDS in babies that are placed on their backs (important thing being that they are on their back)2,3. Some meta-analysis think that it warrants further analysis because it decreases arousability1. Some evidence suggests that swaddling increases SIDs risk over the age of 6 months and therefore consideration should be giving to discontinuing it at that point3.
References
1.
Dixley, A. & Ball, H. L. The effect of swaddling on infant sleep and arousal: A systematic review and narrative synthesis. Frontiers in pediatrics 10, 1000180 (2022).
2.
Oster, E. Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. (Penguin Books, 2020).
3.
Pease, A. S. et al. Swaddling and the Risk of Sudden Infant Death Syndrome: A Meta-analysis. Pediatrics 137, e20153275 (2016).