Brownish discharge can be dangerous if it happens while you are pregnant. It can mean that you have a placenta previa, which is when the placenta is overlying the cervical opening. Any time you have sex, there may be brown discharge or even bright red bleeding. It can be detected on ultrasound and, if the placenta does not migrate upwards in the uterus, you will need to have a cesarean section as a vaginal birth would be extremely dangerous.
Brown discharge between periods can mean that you have uterine polyps on the inside of the uterus. These are benign polyps that can grow in the uterus, in the muscle of the uterus, or on the outside of the uterus. When they are on the inside of the uterus, they can mean you have heavier periods or that you have bleeding or spotting between periods. Polyps that are inside the uterine lining can be removed during a hysteroscopy or a dilatation and curettage (D and C). As mentioned, they are completely benign and do not mean you have cancer.
Brown discharge after menopause can also be dangerous. Any type of bleeding or spotting after menopause can be a sign of uterine cancer. It means you should see your doctor in order to find out the cause of the vaginal bleeding. A hysteroscopy or dilatation and curettage may be performed and a biopsy can be taken to identify any cancerous cells that may be present. If they are found, it means you will have to have a hysterectomy to remove the cancer and possibly may need to have chemotherapy and radiation therapy.
If there is brown discharge during pregnancy, it can also mean you have a condition known as abruptio placentae or an abrupted placenta. It means that the lateral margins of the placenta have torn away from the uterine wall and have begun to bleed. A small amount of bleeding is not dangerous but should still be monitored by your obstetrician. If the flow increases, it could mean that the abruption is getting bigger and the blood flow to the fetus may be compromised. In such cases, it could be an obstetrical emergency necessitating bed rest and a possible cesarean section, even if it means the baby is going to come early. A complete abruption means the placenta has separated completely from the uterus and the baby may die if not delivered immediately.
If the brown discharge does not go away after pregnancy, it may mean that you have retained placental fragments from your pregnancy that are continually bleeding with old blood coming out of the cervix. The bleeding after pregnancy usually lasts for up to six weeks but if it lasts longer than this, you may need to have a dilatation and curettage to scrape out the placental fragments so that the spotting will stop. See your obstetrician if the bleeding and spotting do not go away.