21 weeks belongs to the middle of pregnancy, the state of placenta previa can be relieved by paying more attention to rest, reducing activities, medication and other ways. 1. Rest: If you have placenta previa, you need to pay attention to whether there are bleeding symptoms, and at this time you need to pay attention to rest, do not exercise strenuously, and overwork. 2. Reduce activities: If placenta previa is accompanied by bleeding, it is recommended to stay in bed and reduce activities to avoid excessive bleeding. 3. Medication: For pregnant women who are at risk of miscarriage, medication to inhibit contractions and medication for fetal lung maturation should be given when necessary. For example, indomethacin, dexamethasone and so on. Placenta previa, need to actively diagnosis and treatment, do not blindly use their own medicine, in order to avoid adverse effects.