To explore the association between inter-pregnancy intervals and placenta previa and placenta accreta spectrum among women who had prior cesarean deliveries with respect to maternal age at first cesarean delivery.This retrospective study included clinical data from 9981 singleton pregnant women with a history of cesarean delivery at 11 public tertiary hospitals in seven provinces of China between January 2017 and December 2017. The study population was divided into four groups (<2, 2-5, 5-10, ≥10 years of the interval) according to the inter-pregnancy interval. The rate of placenta previa and placenta accreta spectrum among the four groups was compared, and multivariate logistic regression was used to analyze the relationship between inter-pregnancy interval and placenta previa and placenta accreta spectrum with respect to maternal age at first cesarean delivery.Compared to women aged 30-34 years old at first cesarean delivery, the risk of placenta previa (aRR, 1.48; 95% CI, 1.16-1.88) and placenta accreta spectrum (aRR, 1.74; 95% CI, 1.28-2.35) were higher among women aged 18-24. Multivariate regression results showed that women at 18-24 with <2 years intervals exhibited a 5.05-fold increased risk for placenta previa compared with those with 2-5-year intervals (aRR, 5.05; 95% CI, 1.13-22.51). In addition, women aged 18-24 with less than 2 years intervals had an 8.44 times greater risk of developing PAS than women aged 30-34 with 2 to 5 years intervals (aRR, 8.44; 95% CI, 1.82-39.26).The findings of this study suggested that short inter-pregnancy intervals were associated with increased risks for placenta previa, and placenta accreta spectrum for women under 25 years at first cesarean delivery, which may be partly attributed to obstetrical outcomes.