Is there a reason?

Gabriella • 21 🥂🍷• Future early childhood educator • Alice Cooper fanatic 👁‍🗨👁‍🗨🐍• MCC '18 • In love with my boyfriend • 8-2-16 😍🔐❤️🌎💍
Is there a specific reason why you have to start your birth control the Sunday of the week you're on your period?