The vast majority of sexually experienced women in the United States have used contraceptives at some point in their lives, and a substantial amount of these women have, or are, using contraceptives containing progestin, a synthetic hormone. Progestin partly prevents pregnancy by somehow causing changes in cervical mucus, such as increasing its viscosity so that it is hostile to sperm. The composition of cervical mucus is of scientific interest because the amount of different structural proteins present in mucus likely changes depending on the stage of the menstrual cycle, and is still poorly understood, partly because mucus and its primary structural protein mucin is difficult to collect.