CXCL12 and placenta praevia: The findings demonstrated that the levels of CXCL12, CXCR4, and CXCR7 in placental tissues of the patients with placenta previa exhibited no difference in age, smoking history, and birth history (all P > 0.05), and a significant difference was witnessed in the cases of scar uterus, history of pelvic inflammation, history of cesarean section, and history of abortion (all P < 0.05) (Table 2).