According to WebMD, a bloody show occurs during the first stage of labor, which can last up to 20 hours. A bloody show typically begins when a woman's contractions are approximately three minutes apart and continues until the cervix dilates to 10 centimeters, after which contractions are two minutes apart.
Mayo clinic explains that the bloody show can begin as light spotting early as the 37th week of pregnancy, but it is important for pregnant women to consult with a physician if the bleeding is as heavy as a regular menstrual flow. As the cervix begins to widen, it is common for women to experience an increase in vaginal discharge. During the gestation period, the cervix is protected by thick mucus, also referred to as the mucus plug. Loss of the mucus plug is typically a sign that labor is near.