<P> Infrequent or irregular ovulation is called oligoovulation . The absence of ovulation is called anovulation . Normal menstrual flow can occur without ovulation preceding it: an anovulatory cycle . In some cycles, follicular development may start but not be completed; nevertheless, estrogens will be formed and stimulate the uterine lining . Anovulatory flow resulting from a very thick endometrium caused by prolonged, continued high estrogen levels is called estrogen breakthrough bleeding . Anovulatory bleeding triggered by a sudden drop in estrogen levels is called withdrawal bleeding . Anovulatory cycles commonly occur before menopause (perimenopause) and in women with polycystic ovary syndrome . </P> <P> Very little flow (less than 10 ml) is called hypomenorrhea . Regular cycles with intervals of 21 days or fewer are polymenorrhea; frequent but irregular menstruation is known as metrorrhagia . Sudden heavy flows or amounts greater than 80 ml are termed menorrhagia . Heavy menstruation that occurs frequently and irregularly is menometrorrhagia . The term for cycles with intervals exceeding 35 days is oligomenorrhea . Amenorrhea refers to more than three to six months without menses (while not being pregnant) during a woman's reproductive years . </P> <P> The menstrual cycle can be described by the ovarian or uterine cycle . The ovarian cycle describes changes that occur in the follicles of the ovary whereas the uterine cycle describes changes in the endometrial lining of the uterus . Both cycles can be divided into three phases . The ovarian cycle consists of the follicular phase, ovulation, and the luteal phase, whereas the uterine cycle consists of menstruation, proliferative phase, and secretory phase . </P> <P> The follicular phase is the first part of the ovarian cycle . During this phase, the ovarian follicles mature and get ready to release an egg . The latter part of this phase overlaps with the proliferative phase of the uterine cycle . </P>

What are the two parts of the menstrual cycle