The most common cause of blood in the panties at five weeks of pregnancy is preterm miscarriage, but the possibility of ectopic pregnancy cannot be ruled out either, which requires observation and differentiation to be sure. Ultrasound at five weeks of pregnancy cannot monitor the gestational sac yet, so you can only pay attention to the size of the bleeding and clinical symptoms to see if there is any stomach pain. If intrauterine pregnancy is not confirmed before, birth control is usually not recommended. If an ultrasound is performed to detect an intrauterine pregnancy, the progesterone level should be checked. If the progesterone level is low, oral progesterone or intramuscular progesterone injections can be used to preserve the pregnancy, but this method should not be used until an intrauterine pregnancy is confirmed. If there is no intrauterine gestational sac in the ultrasound, the pregnancy is considered ectopic and requires timely hospitalization to avoid serious development of the condition.