Increased stress, psychosocial problems, economic disadvantages, and lack of prenatal care are proposed to explain discrepancies in the outcome of unintended pregnancies. Studies of maternal intention and pregnancy outcomes have yielded varied results. Objective is to review studies of the risk of low birth weight (LBW)/preterm births (PTB) associated with unintended pregnancies ending in a live birth. We reviewed studies reporting on maternal intentions and outcomes from Medline, Embase, CINAHL, and bibliographies of identified articles. An unintended pregnancy was further classified as mistimed (not intended at that time) or unwanted (not desired at any time). Studies reporting an association between pregnancy intention and any of the outcomes were included. Study quality was assessed for biases in selection, exposure assessment, confounder adjustment, analyses, outcomes assessment, and attrition. Unadjusted and adjusted data from included studies were extracted by two reviewers. There were significantly increased odds of LBW among unintended pregnancies [odds ratio (OR) 1.36, 95% confidence interval (CI) 1.25, 1.48] ending in a live birth. Within the unintended category, mistimed (OR 1.31, 95% CI 1.13, 1.52) and unwanted (OR 1.51, 95% CI 1.29, 1.78) pregnancies were associated with LBW. There were statistically significantly increased odds of PTB among unintended (OR 1.31, 95% CI 1.09, 1.58), and unwanted (OR 1.50, 95% CI 1.41, 1.61) but not for mistimed (OR 1.36, 95% CI 0.96, 1.93) pregnancies. Unintended, unwanted, and mistimed pregnancies ending in a live birth are associated with a significantly increased risk of LBW and PTB.