Corpus luteum follicle-stimulating hormone (FSH). A new corpus luteum develops with each menstrual cycle. The "corpus luteum" develops from an ovarian follicle during the luteal phase of the menstrual cycle or oestrous cycle, following the release of a secondary oocyte from the follicle during ovulation. The follicle first forms a corpus hemorrhagicum before it becomes a corpus luteum, but the term refers to the visible collection of blood, left after rupture of the follicle, that secretes progesterone. While the oocyte (later the zygote if fertilization occurs) traverses the Fallopian tube into the uterus, the corpus luteum remains in the ovary. The corpus
Menstrual cycle greatly decreases the release of FSH, which makes combined hormonal contraceptives more effective at inhibiting follicular development and preventing ovulation. Estrogen also reduces the incidence of irregular breakthrough bleeding. Several combined hormonal contraceptives—the pill, NuvaRing, and the contraceptive patch—are usually used in a way that causes regular withdrawal bleeding. In a normal cycle, menstruation occurs when estrogen and progesterone levels drop rapidly. Temporarily discontinuing use of combined hormonal contraceptives (a placebo week, not using patch or ring for a week) has a similar effect of causing the uterine lining to shed. If withdrawal bleeding is not desired, combined hormonal contraceptives