Question: How does your body know when you are ready to start your period

Sara Falcone answered on 17 Nov 2015:

Hello 🙂

There are lots of factors that induce a girl’s first period (that it is called menarche). We have genetic factors, environmental factors and nutritional factors. We don’t really know exactly what triggers it, but in the couple of years before there is a higher production, for 2 or 3 years before the first period, of an hormone (the estrogen) that stimulates the growth of the uterus (and other bits :P). When you have a fluctuation of this hormone (and the production of others) you have your first period.
As for a monthly period, it’s pretty much all about the different hormones that are released by your ovaries and uterus at the different points of your egg production cycle.