Dark brown spotting during pregnancy can be concerning, but it doesn't always indicate a miscarriage. It could be due to implantation bleeding, cervical irritation, or hormonal changes. However, since you mentioned that no heartbeat was detected during your ultrasound, it's important to consult your healthcare provider for further evaluation and guidance. They may recommend additional tests like another ultrasound or blood work to determine the status of your pregnancy. While waiting for your appointment, try to stay calm and avoid unnecessary stress as it can impact both you and the baby. Remember that every pregnancy is different, and only a medical professional can provide an accurate diagnosis and appropriate advice based on your specific situation.