Our study is testing an investigational birth control pill that is not on the market. The pill contains both estrogen and progestin. The estrogen used in the study pill may cause fewer side effects than the estrogen used in pills that are currently on the market. This study will find out how effective this pill is at preventing pregnancy and learn more about side effects and bleeding patterns during pill use. Approximately 2000 women will take part in this study at different research centers across the US.