What natural hormones do

Everything to do with your menstrual cycle and pregnancy is controlled by a gland in your brain called the pituitary gland.

This gland releases tiny amounts of substances every month which cause the ovaries to react and produce sex hormones, estrogen and progesterone. Estrogen is made by the ovaries during the first two weeks of your cycle and its job is to prepare your body for the arrival of an egg, ready to be fertilised by sperm. For this to happen, the egg has to leave the place where it was made (inside the ovary) and come to the surface. It travels to the surface of the ovary in a tiny bubble (the follicle) which then pops open to release the mature egg. This happens round about the middle of the cycle and is called ovulation. The egg then continues its journey towards the womb.

Meanwhile, the remainder of the bubble remains on the surface of the ovary. It then begins to produce large amounts of progesterone and estrogens. The function of progesterone is to maintain a pregnancy should it occur.

At the same time, the progesterone is preparing the lining of the womb to receive the fertilised egg - if there is one. It transforms the womb lining (which has been thickened by the estrogen) to hold and nurture the egg. However, most months, fertilisation doesn't take place. Therefore, this ready-made, thicker womb lining is not needed and the mature egg is dissolved in the womb. At this point, the levels of both hormones go down. This in turn causes the womb lining to dissolve and vanish through the cervical canal. That's what your period is, the womb lining which is shed every month when your estrogen level drops. By the end of your period, the cycle is over and then the whole story starts again.