A progesterone value of less than 1ng/ml is a sign that menstruation is imminent. After ovulation, if a woman is not pregnant, when progesterone continues to rise and reaches its highest level, it will begin to fall along with estrogen, causing withdrawal bleeding, which usually reaches its lowest level before the onset of menstruation, causing menstruation to occur, so if progesterone is less than 1ng/ml, it means that menstruation is about to occur. The level of progesterone is important for a woman’s health, and regular testing and consultation with a specialist is required when necessary.