Miscarriage after the third week of pregnancy may be caused by low progesterone, chromosomal abnormality of the embryo or external factors, etc. It is necessary to determine whether the miscarriage is clean, and if it is not clean, the uterus should be purged. 1. Low progesterone: Luteal insufficiency may lead to low progesterone, which in turn leads to the endometrium not having enough progesterone to stimulate growth, thus leading to miscarriage. If this is the case, you need to make sure that the miscarriage is not clean, if it is clean, then pay attention to rest, replenish sufficient nutrition, etc. But if it is not clean, then you need to make sure that the miscarriage is not clean. However, if the abortion is not clean, then you need to perform additional sterilization surgery. 2. Chromosomal abnormality of the embryo: If the embryo itself has abnormal chromosomes, spontaneous abortion can be caused by growth and developmental obstruction. After the spontaneous abortion, you need to observe the chorionic tissue to determine whether the abortion is clean or not. If it is not clean, it is necessary to carry out timely clearance surgery; if it is clean, pay attention to supplemental nutrition, pay attention to rest, etc., before the next pregnancy, feasible pre-pregnancy examination. 3. External factors: after three weeks of pregnancy, if the fall, mental trauma and other external factors cause miscarriage, also need to observe the flow out of the chorionic tissue and menopausal days whether it is consistent to determine whether it is clean, if it is clean pay attention to the postpartum repair can be; but if it is not clean, you need to promptly perform the operation of the uterus. After three weeks of pregnancy, you need to go to the hospital in a timely manner, in addition to determine whether the abortion is clean, but also need to improve the relevant examination to clarify the cause of the abortion, in order to prepare for the next conception.