Explaining the curvilinear relationship between age at first birth and depression among women.

Recent research suggests that the effect of age at first birth on mental health for women is curvilinear, with first births at both young (age 20 and younger) and older ages (after age 30) being positively associated with psychological distress. Scholars have theorized that accumulated disadvantages and physical health problems associated with age at first birth explain this pattern, although empirical support for these explanations has varied. Using data from the US National Longitudinal Survey of Youth 1979, this study provides evidence of an alternative explanation for this curvilinear relationship through its focus on: 1) the relationship between deviations from expected age at first birth and women's actual age at first birth, and 2) the effect deviations from expected age at first birth have on mental health. Results indicate that deviating from their expected age at first birth results in higher levels of depressive symptoms for women in midlife who transition into parenthood both earlier and later than expected. These deviations from expected birth timing account for the upward trend in depressive symptoms at older ages of first birth, but explain only a small amount of the higher levels of depressive symptoms at younger ages.