The causes of brown discharge during pregnancy are not exactly the same among different women. 1. A small amount of brown discharge in early pregnancy may be due to insufficient progesterone level in the body or endometritis, which may cause a small amount of bleeding that stays in the uterine cavity for too long as old bleeding. 2. The woman may have irregular vaginal bleeding after pregnancy, manifested as brown discharge. 3, after the middle and late pregnancy, if there is brown discharge, there may be a problem of placenta previa, you can go to the hospital and do ultrasound examination for clear diagnosis.