BackgroundCurrently, there is no consensus regarding the relationship between neonatal transfer and duration of hospitalization in cases of impaired mother-infant bonding (MIB). This study aimed to determine whether neonatal transfer and duration of hospitalization of newborns increase the risk for impaired MIB. MethodsThe MIB Scale was used to assess impaired MIB 1 year after delivery, using data from the Japan Environment and Children's Study. A score ≥ 5 points indicated impaired MIB. Multiple logistic regression analyses were performed to estimate the association between neonatal transfer and duration of hospitalization of newborns with the risk of impaired MIB. ResultsA total of 66,402 pregnant women were included in the study. The overall incidence rate of impaired MIB was 11.2 %. The mean duration of hospitalization of newborns was 7.1 ± 6.4 days. After adjusting for potential confounders, neonatal transfer (adjusted odd ratio (OR): 1.13 [95 % confidence interval (CI)), 1.01–1.27]) and duration of hospitalization of newborns (adjusted OR 1.007; 95 % CI 1.003–1.010) were associated with impaired MIB. The area under the receiver operating characteristic curve for the duration of hospitalization of newborns for impaired MIB was 0.53. LimitationsMaternal childhood abuse and neglect history were not evaluated, and information regarding whether the infants were admitted to the neonatal intensive care unit was unavailable. ConclusionsJapanese women whose newborns underwent neonatal transfer should be followed up for at least 1 year after delivery, regardless of the duration of hospitalization of newborns.