What most women don't know is that one of the first signs of PMS is irregular menstrual cycles. Let's make sure you fully understand how this works clinically. The menstrual cycle is a process that prepares the uterus for pregnancy. It's natures way of preparing the body to secure the egg during the fertilization process. Conversely, if the time isn't right, the uterus begins a process of cleaning out the area so that the process can start all over again next month.
Most women have relatively regular periods.
The length of a normal menstrual cycle varies anywhere from three to five weeks, with menstruation lasting between three to seven days. Let's take a look at the actual physiology that takes place during your cycle. Menstruation is controlled by a series of hormonal interactions between the brain and the ovaries. FSH triggers the growth of follicles in the ovary where the egg is stored. As the follicle grows, it secretes estrogen in increasing amounts.