<P> Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal). The average blood loss during menstruation is 35 milliliters with 10--80 ml considered normal . Women who experience Menorrhagia are more susceptible to iron deficiency than the average person . An enzyme called plasmin inhibits clotting in the menstrual fluid . </P> <P> Painful cramping in the abdomen, back, or upper thighs is common during the first few days of menstruation . Severe uterine pain during menstruation is known as dysmenorrhea, and it is most common among adolescents and younger women (affecting about 67.2% of adolescent females). When menstruation begins, symptoms of premenstrual syndrome (PMS) such as breast tenderness and irritability generally decrease . Many sanitary products are marketed to women for use during their menstruation . </P> <P> The proliferative phase is the second phase of the uterine cycle when estrogen causes the lining of the uterus to grow, or proliferate, during this time . As they mature, the ovarian follicles secrete increasing amounts of estradiol, and estrogen . The estrogens initiate the formation of a new layer of endometrium in the uterus, histologically identified as the proliferative endometrium . The estrogen also stimulates crypts in the cervix to produce fertile cervical mucus, which may be noticed by women practicing fertility awareness . </P> <P> The secretory phase is the final phase of the uterine cycle and it corresponds to the luteal phase of the ovarian cycle . During the secretory phase, the corpus luteum produces progesterone, which plays a vital role in making the endometrium receptive to implantation of the blastocyst and supportive of the early pregnancy, by increasing blood flow and uterine secretions and reducing the contractility of the smooth muscle in the uterus; it also has the side effect of raising the woman's basal body temperature . </P>

What hormone is most important in the proliferative phase of the uterine cycle