The terms mistimed pregnancy (MP) and unwanted pregnancy (UWP) refer to a woman's intentions regarding childbearing. Determinants for each type of pregnancy have not been well understood. The present study aims to investigate whether MP and UWP have different sets of psychosocial determinants compared to intended pregnancy, with a particular emphasis on any difference in the history of maternal psychiatric diagnosis. Using an ongoing birth cohort study, we consecutively enrolled parturients who were at mid-pregnancy (n = 780) and were expected to give birth at either of our two research sites. MP and UWP were defined according to previous studies. To avoid multiple testing, we adopted multinomial logistic regression to estimate the independent contribution of the determinants while simultaneously allowing for other variables. The dependent variable in the model had three classes: Intended pregnancy, MP and UWP. Determinants of MP included younger age (<25 years: OR = 2.6), currently working (OR = 1.6), and history of major depression (OR = 2.0). Determinants for UWP were multiparity (OR = 3.9), short (≤12 years, OR = 1.7) and long period of education (≥17 years, OR = 3.3), history of anxiety disorder (OR = 2.5), currently working (OR = 0.6) and high income (≥8 million JPY, OR = 0.4). Different sets of psychosocial determinants contribute to formulate MP and UWP. A history of mental illness plays a role in predicting pregnancy intention.