Mental health-related quality of life and the timing of motherhood: a 16-year longitudinal study of a national cohort of young Australian women.

Purpose: We examine timing of motherhood in a longitudinal cohort of young Australian women, and its relationship with mental health-related quality of life (SF-36 MHI-5), and with sociodemographic, health behaviour and health-related variables.

Methods: We analysed longitudinal self-report data from a nationally representative cohort of 10,332 Australian women born 1973-1978, surveyed 6 times between 1996 (aged 18-23) and 2012 (aged 34-39).

Results: Group-based trajectory modelling identified four groups. Normative Mothers (46%, mean age at motherhood 30.5 years) made the transition to motherhood close to the Australian median age. Early Mothers (25%, 25.2 years) and Very Early Mothers (7%, 20.0 years) made this transition earlier; Not Mothers (22%) had not given birth. Generalised linear mixed models showed that all groups improved mean MHI-5 scores over time. Patterns of group differences were complex: Normative and Early Mothers scored consistently highest; Very Early Mothers scored lowest at most surveys; Not Mothers' scores increased relative to others over time. Most effects disappeared after adjustment for confounders. Early and Very Early Mothers showed multiple indicators of social disadvantage, while Not Mothers had very low rates of marriage.

Conclusions: Timing of motherhood is embedded in sociodemographic and personal contexts. Women with socioeconomic advantages were characterised by higher mental health-related quality of life and later transition to motherhood, but adjustment for relative advantage attenuated differences in mental health-related quality of life. The overall findings suggest a pattern of positive adaptation to circumstances, with mental health-related quality of life improving through early adulthood regardless of timing of motherhood.