Association of late-onset postpartum depression of mothers with expressive language development during infancy and early childhood: the HBC study.

Background: While it has been implied that an infant's exposure to maternal postpartum depression (PPD) may be associated with delayed development of expressive language, it remains unclear whether such a delay persists into childhood and whether the onset of PPD onset-early (within 4 weeks after childbirth) vs. late (between 5 and 12 weeks postpartum)-is relevant in this context.

Objective: To examine whether children of mothers with early- or late-onset PPD have reduced expressive language scores during infancy and early childhood (up to 40 months of age).

Methods: This longitudinal, observational study was conducted as a part of the Hamamatsu Birth Cohort for Mothers and Children (HBC Study), a population-representative sample in Japan. A total of 969 neonates and their mothers were included in the analysis.

Exposures: Early- and late-onset PPD was measured using the Edinburgh Postnatal Depression Scale.

Main Outcomes and Measures: Expressive language development was measured using the Mullen Scales of Early Learning. Six points over time were monitored (10, 14, 18, 24, 32, and 40 months postpartum). The relationship between the exposure variable and any change in expressive language score was evaluated using multiple linear regression analysis and growth curve analysis, both adjusted for covariates.

Results: Results from the adjusted regression analysis showed that children of mothers with late-onset PPD had significantly lower expressive language scores at 18 months of age and beyond, with a score reduction of approximately 0.6 standard deviations from the reference value at 40 months of age (95% CI [-0.888 to -0.265], p  < .001). This association was confirmed on growth curve analysis, which revealed a significant, monotonic decline of expressive language development between 10 and 40 months of age among children of mothers with late-onset PPD, but not among children of mothers with early-onset PPD.

Conclusion: Exposure to late-onset PPD may lead to a persistent decline in the rate of expressive language development in offspring during infancy and early childhood, highlighting the significance of monitoring for late-onset PPD to facilitate early detection and intervention.