It is not uncommon for pregnant women to experience brown mucus-like discharge and occasional spotting during the second trimester, including at 21 weeks. This can be caused by various factors such as hormonal changes, cervical irritation, or even old blood being expelled from the body. In most cases, this type of discharge is considered normal and does not pose a threat to the pregnancy. However, it is always important to consult with your healthcare provider to rule out any potential complications or underlying issues. They will be able to evaluate your specific situation and provide appropriate guidance based on your individual circumstances. If you notice any other concerning symptoms such as heavy bleeding, severe cramping, or fever, it is recommended that you seek immediate medical attention. Remember that every pregnancy is unique, so trust your instincts and reach out to your healthcare provider whenever you have concerns about your well-being or the health of your baby.