The first day of the menstrual period begins another cycle of follicle and egg maturation, ovulation and preparation of the uterus for the potential arrival of a fertilized egg. The characteristics of the first day of the menstrual period are related to the changes necessary for the beginning of another reproductive cycle. Deviations from normal characteristics may indicate problems within the reproductive system.
Menstrual Bleeding
Sometimes the first day of a menstrual period is characterized by light bleeding, but many women have normal menstrual bleeding starting on Day 1. Bleeding that's too heavy on Day 1, with clots and soaking through pads or tampons in a few hours, may indicate that the uterine lining is growing too thick between periods. Normal blood loss during a period is .5 oz. to 2.5 oz., according to the Mayo Clinic. A lining that's too thick can interfere with implantation and may occur in people with hormonal imbalances including polycystic ovary syndrome. Bleeding that's very heavy may also be caused by fibroids or polyps in the uterus that can interfere with implantation of an embryo.
Abdominal Cramping
Many women experience cramping every month, especially on the first day of the menstrual cycle. Cramping is caused by prostaglandin release and by the contractions of the uterus as it expels the lining; prostaglandins are hormones produced in the cells of the uterus during menstruation. Cramping is normal as long as it's mild and doesn't last more than a day or two. Prolonged or severe cramping may indicate endometriosis, growth of the uterine lining outside the uterus in the pelvic cavity. Cramping can be treated with anti-prostaglandin medications such as aspirin or ibuprofen, Science Encyclopedia says.
Hormonal Changes
Estrogen and progesterone levels drop abruptly as Day 1 of the menstrual cycle begins. Hormonal changes can cause mood swings, irritability and fatigue. Dropping progesterone levels may be the cause of bloating, breast tenderness and food cravings at the time of menstruation. If hormonal levels don't drop to low levels, high estrogen or progesterone levels may keep a new follicle from developing. Rising prostaglandin levels cause cramping and in some cases, nausea, diarrhea and vomiting, the Mayo Clinic says.
