This study investigated the association between maternal home blood pressure (HBP) trajectory during pregnancy and infant birth weight. A total of 755 pregnant women were included in this prospective cohort study. A group-based trajectory model identified six trajectory groups for home systolic blood pressure (SBP), diastolic BP (DBP), and mean arterial pressure (MAP). Next, the association of HBP trajectory groups with infant birth weight was evaluated using a general linear model considering potential confounding factors. For home SBP and MAP, the trajectory groups with a low-steep J-curve, moderate J-curve, little high J-curve, and high J-curve were significantly associated with lower infant birth weight than the low-J-curve group. Among the trajectory groups for home DBP, the moderate-steep J-curve, little high J-curve, and high J-curve were significantly associated with lower infant birth weight than the group with low-J-curve. The effect sizes of the trajectory groups varied in infant birth weight from -0.21 standard deviations (SDs) (95% confidence interval (CI): -0.42 to -0.01 SD) to -1.13 SD (95% CI: -1.54 to -0.72 SD). In the analyses of infant birth weight in grams, effect sizes that were significantly associated with infant birth weight varied from -84 g (95% CI: -167 to -1 g) to -567 g (95% CI: -732 to -402 g). Trajectory groups with a moderate-reverse J-curve for home SBP, DBP, and MAP were not significantly associated with infant birth weight. Maternal HBP trajectory during pregnancy was an indicator of infant birth weight. Further studies evaluating the associations between HBP during pregnancy and other perinatal outcomes are needed.