Good to Know: Facts About Menstruation Period facts...interesting girl info The word "menstruation" comes from , the Latin word for "month." That gives you a big clue to what it menses ’ s all about. Or if you ’ ve heard friends talk about "that time of the month," you can probably guess that women go through menstruation about every month. A menstrual cycle is the time between the first day of one period and the first day of your next period. The amount of time it takes for menstruation to happen is about a month (the average cycle lasts 28 days). One complete cycle is made up of several phases. You are born with all the eggs you ’ll ever have! Over your lifetime, you will release about 500 mature eggs. The number of eggs that you have depends on your age. The highest number is actually found before you are born! Here ’ s how it happens: When you were a 20-week-old female fetus (still in your mother ’ s uterus) you had approximately 7 million eggs. At birth, the number decreased to about 2 million. By the time you enter puberty, you have between 300,000 and 500,000 eggs. Only between 400 and 500 will ripen into mature eggs during your life. Read about menstruation and learn helpful tips for dealing with your period from BeingGirl.