BackgroundIn England, the rate at which infants enter care varies considerably by local authority, with little evidence on what drives these differences. Decisions instigating infant entry into care may be triggered by child protection concerns arising from parental ill-health or risky behaviour from pregnancy onwards. Main AimWe explored the extent to which adversity indicated within women’s hospitalisation history, pre-delivery, explained differences in rate of infant entry into care between local authorities. Methods/ApproachCombining data from several sources (Office for National Statistics Population Estimates, Public Health England Fingertips, 2011 Census, Children Looked After Return, and Hospital Episode Statistics), we derived population-level predictors for entry into care (i.e. local case-mix) for 131 English local authorities from 2006/07 to 2013/14. Our primary outcome was rate of infant entry into care. We used linear mixed-effects models to analyse the relationship between the outcome and percentage of live births with maternal history of adversity-related hospital admissions (i.e. any admission indicating substance misuse, mental ill-health, or violence, up to 36 months pre-delivery), adjusting for other case-mix measures. ResultsRate of infant entry into care (mean: 85.16 per 10,000 [min-max: 0.00-318.51]) and percentage of live births with maternal history of adversity-related hospital admissions (4.62%, [0.52-16.19%]) varied greatly by local authority. Prevalence of maternal adversity accounted for 24% of variation in rate of entry (95% CI: 14-35%). After adjustment, there was evidence that a percentage point increase in prevalence of maternal adversity - both over time and between local authorities - is associated with an extra 2.56 infants, per 10,000, entering care (1.31-3.82). Conclusion Prevalence of maternal adversity prior to birth helps to explain differing rates of infant entry into care among local authorities. Further research using individual-level linked parent-child data is required to ascertain whether interventions to reduce maternal adversity before birth would decrease rate of infant entry into care.