Aim: While delayed initiation of childbearing is associated with adverse perinatal outcomes, whether or not risk persists and whether interpregnancy interval (IPI) affects the subsequent pregnancy remains unclear. Objectives: To examine second-pregnancy perinatal outcomes for women initiating childbearing age ≥30 compared to those initiating childbearing aged 20-29, specifically examining the distribution of adverse perinatal outcomes, and their associations with the interpregnancy interval. Methods: Retrospective cohort study using the Missouri maternally linked files 1978-1997. Perinatal outcomes included fetal death, low birthweight, preterm birth and small-for-gestational age. Predictor variables included maternal age at first pregnancy and IPI between the first and second pregnancy. Results: With an increasing maternal age at first pregnancy, rates of very low birthweight (P = 0.0095), preterm delivery (P = 0.0126), moderately preterm (P = 0.0458), and extremely preterm (P = 0.0008) in the second pregnancy increased, while the rate of small-for-gestational age (P < 0.0001) declined. Interpregnancy intervals <6 and ≥60 months were associated with a higher rate of adverse outcomes after controlling for maternal age at first pregnancy. Intervals of 12-17 months had the lowest rate of adverse outcomes for mothers 35+. Maternal age ≥35 years at first pregnancy and IPI <6 months were independent risk factors for an adverse outcome in the second pregnancy, however no statistical interaction between these factors was observed. Conclusion: Delayed initiation of childbearing is associated with a persistent risk of adverse perinatal outcomes in the second pregnancy, with a short IPI contributing to this risk. As numbers of women delaying childbearing beyond age 30 increase, providers should consider these risks in counseling women about their reproductive plans. © 2008 Japan Society of Obstetrics and Gynecology.