Maternal nutrition can have a profound effect on fetal growth, development, and subsequent infant birth weight. Preconception dietary patterns have not been assessed in relation to perinatal outcomes. The objectives of this study were to identify associations between maternal dietary patterns in the 12 mo before conception on fetal growth and preterm delivery. Preconception food frequency data were collected retrospectively in 309 women. Dietary patterns were derived using factor analysis. Perinatal outcomes were collected at delivery with birth weight data calculated into percentiles to assess small and large for gestational age and preterm delivery at <37 wk. Three dietary patterns were identified: 1) high-protein/fruit (characterized by fish, meat, chicken, fruit, and some whole grains); 2) high-fat/sugar/takeaway (takeaway foods, potato chips, refined grains); and 3) vegetarian-type (vegetables, legumes, whole grains). A 1-SD increase in the scores on the high-protein/fruit pattern was associated with decreased likelihood of preterm birth (adjusted OR: 0.31; 95% CI: 0.13, 0.72; P = 0.007), whereas the reverse direction was apparent for the high-fat/sugar/takeaway pattern (adjusted OR: 1.54; 95% CI: 1.10, 2.15; P = 0.011). A 1-SD increase in the scores on the high fat/sugar/takeaway pattern was also associated with shorter gestation (adjusted regression coefficient: -2.7; 95% CI: -4.3, -1.1; P = 0.001) and birth length (adjusted regression coefficient: -0.5; 95% CI: -0.8, -0.1; P = 0.004). Nutrition before pregnancy is associated with perinatal outcomes. A dietary pattern containing several protein-rich food sources, fruit, and some whole grains is associated with reduced likelihood for preterm delivery, whereas a dietary pattern mainly consisting of discretionary items is associated with preterm delivery, shorter birth length, and earlier gestation. Poor dietary behaviors in the periconceptional period could be altered to promote behavior change in dietary intake to improve perinatal outcomes and the long-term health of the child.