To describe the structure of networks in a cohort of mothers and to analyze associations of social network characteristics and norms with infant sleep practices.

We recruited a prospective cohort of mothers with infants <6 months of age from January 2015 to December 2016. Mothers completed a survey about their personal social networks and infant care practices. Latent class analysis identified unobserved network types. Binary statistics and path analysis were performed.

Overall, 402 mothers were surveyed. Latent class analysis identified 2 a priori unknown social network types: “exclusive” (restricted) and “expansive.” Mothers who were black, younger, unmarried, less educated, and of lower socioeconomic status were more likely to have exclusive networks than expansive networks. Mothers with exclusive networks were more likely to be exposed to the norm of soft bedding (P = .002). Exposure to norms of non-supine infant placement, bedsharing, and soft bedding use within one's network was associated with engaging in these practices (P < .0001 for each). First-time mothers were more likely to pay attention to a non-supine norm and place infants in a non-supine position. Black mothers and first-time mothers were more likely to pay attention to the norm and use soft bedding.

Both the type of networks mothers have and the norms regarding infant sleep practices that circulate within these networks differed by race. Network norms were strongly associated with infant sleep practices and may partially explain the racial disparity therein.