The first thing to rule out in this case is the possibility of ectopic pregnancy, which is when a fertilized egg lays outside the uterine cavity. In clinical practice, the common site is the fallopian tube. Since the fallopian tube is relatively small, the fertilized egg will grow in it, and the patient will feel pain in the small of the stomach on one side and also have a small amount of bleeding. In addition to the symptoms of ectopic pregnancy, pre-eclampsia and incomplete miscarriage, which also occur when the embryo does not adhere firmly to the uterine wall, may also occur. Pre-eclampsia can occur with a small amount of vaginal bleeding, which can progress to incomplete miscarriage if care is not taken to preserve the pregnancy. In addition to vaginal bleeding, there will be paroxysmal pain in the stomach, so it is important to go to the hospital as soon as possible for an ultrasound to confirm the cause of the condition.