If there is brown blood in the fourth week of pregnancy, there are several possibilities for this condition: the first possibility is preterm miscarriage. Early pregnancy is a superior process, and if the fetus is unstable or the embryo is of poor quality, it can easily lead to preterm miscarriage, which needs to be treated through birth control and rest. The second possibility is to consider whether it is an ectopic pregnancy. Patients with ectopic pregnancy are prone to bleeding and abdominal pain in the early stages. If it is an ectopic pregnancy, it requires hospitalization for treatment and, if necessary, surgery.