What Is A Normal Period? Women Who Started Menstruation As Young Girls Face Early Menopause Before 40, Study Finds

Women unsure about when they should start a family now have another worry to add to their fears: the age when they started their first periods.

Women who experience their first period when they are just 11 years old or younger are more likely to go through menopause in their 30s, a study published Tuesday in the journal Human Reproduction found. Women who start their periods as young girls and never have children later in life are even more likely to undergo premature menopause.

Early menopause is defined as by age 44, but women who got their first period at age 11 or younger were 80 percent more likely to stop having periods before they hit 40 years old. The study found the median age of menopause was 50 and the median age of a first period was 13. About 14.1 percent of the women in the study started their periods at age 11 or younger. The study looked at 51,540 women in Australia, England, Denmark and Japan.

Menopause not only marks the end of a woman's childbearing years, it also comes with uncomfortable symptoms such as hot flashes and fatigue. More seriously, it can increase the risk of polycystic ovary syndrome, heart disease, diabetes and endometriosis.

"Understanding the relationship [between first and last periods] will provide us with the opportunity to monitor or intervene as early as possible," lead author Gita Mishra, a professor of life course epidemiology at the University of Queensland, Australia, told NPR.

The average woman has her period every 28 days, althought some cycles run from 24 to 35 days. Girls can start their periods at age 10, but the average age is 12 years old. Menopause, when the period stops, starts at the age of 50, but it could happen later or earlier. It's all considered normal.

A woman has roughly 480 periods during her lifespan, depending on if she gets pregnant. A period is a sign a woman is not pregnant. The egg enters the fallopian tubes and when pregnancy doesn’t occur, the womb lining falls apart and exits the body through the menstrual flow. Periods typically last three to seven days, during which women can lose up to five tablespoons of blood.

The hormone progesterone is what causes the womb lining to grow thicker and prepare for a fetus.