Low-dose aspirin (LDA) is considered to be the most effective agent to prevent preeclampsia (PE). At present, there is little exploration about the timing of aspirin discontinuation. Most international guidelines default until 36 weeks of gestation or delivery. China Guideline (2020) recommended that aspirin should be preventively used until 26-28 weeks of gestation, but there was little direct evidence. According to the two-stage theory, placental dysplasia before 28 weeks of gestation is the key to developing PE, the significance of aspirin use after 28 weeks of gestation is debatable. If aspirin discontinuation at 28 weeks of gestation is proven to be feasible for preventing preterm PE, it will not only reduce the risk of Perinatal Haemorrhage but also save medical expenses.