Throughout the course of pregnancy, vaginal redness is normal except for late pregnancy when you are about to have an episode, but any time other than that, the presence of brown vaginal discharge is not normal. The most common cause of brown discharge at 16 weeks of pregnancy is preterm miscarriage, followed by a low placenta. This is because until 28 weeks, the placenta is usually still relatively close to the cervical os. At this stage, if a pregnant woman engages in strenuous exercise or has sexual intercourse, it is easy for brown discharge to appear. If it is determined that the blood is coming out of the uterine cavity, and if it is also determined that the placenta is low, it is recommended to hospitalize the baby and pay attention to the bleeding during the whole pregnancy.