During the first half (or preovulatory phase) of a women's cycle, progesterone levels remain relatively low. Following ovulation (the luteal phase), however, the amount of progesterone will increase to help support the implantation of a fertilized egg in the uterus, as well as help maintain a pregnancy by preventing menstruation. Progesterone will also cause a marked warming of the body that is detectable (and measurable) through the technique of basal body temperature charting (read more in the next section on this). Progesterone levels will remain high during your pregnancy.