Testing lifecourse theories characterising associations between maternal depression and offspring depression in late adolescence: the Avon Longitudinal Study of Parents and Children

Background: Maternal depression influences offspring mental health. Yet little is understood about how the duration and timing of maternal depression shapes youth risk for depressive symptoms, which if understood could inform when best to intervene. Consequently, this study aimed to determine how the timing and duration of maternal depression was related to offspring depression in late adolescence, and variations by sex. Methods: We used data from the Avon Longitudinal Study of Parents and Children (a prenatal cohort in the Avon area of England, 1991-2003), n=3,301. We applied a structured lifecourse modelling approach to maternal depression (assessed at thirteen points from prenatal period to adolescence) and late adolescent depressive symptoms (age 21). Lifecourse models assessed were accumulation (sum of timepoints when maternal depression was reported), sensitive periods (each period assessed as one during which maternal depression has a stronger effect) and instability (frequent fluctuations in maternal depression). Results: Female adolescents (n=2,132) had higher SMFQ scores (mean=6.15, SD=5.90) than males (n=1,169, mean=4.87, SD=4.82). Maternal depression was most common in the prenatal period (21.1% males; 22.2% females). For males, accumulation was the most appropriate model; for each additional period of maternal depression, depressive symptoms in late adolescence increased by 0.11 (95% CI: 0.07,0.15, 1-sided p value≤0.001). For females, exposure to maternal depression was associated with increasing depressive symptoms in late adolescence, with the largest effect in mid-childhood (increase of 0.27 units, 95% CI 0.03-0.50, p=0.015 for difference between mid-childhood and other time-periods) and a smaller, equal effect at all other time-periods (increase of 0.07 units per time-period, 95% CI: 0.03-0.12, p=0.002). Conclusions: This study highlights the importance of ongoing maternal depression for the development of depression in offspring through to late adolescence. Because long-term exposure to maternal depression was particularly important, early interventions are warranted.