Understanding the Menstrual Cycle

The menstrual cycle is controlled by two hormones released from the brain, specifically the pituitary gland which releases follicle stimulating hormone (FSH) and lutenising hormone (LH).

This causes an egg cell located in the female reproductive system to grow and mature. 

In response, follicles release oestrogen and cause eggs to grow. This inhibits the production of FSH and increases the release of LH, eventually causing the release of the egg, otherwise known as ovulation. 

Meanwhile the empty follicle releases progesterone to promote the uterus lining to develop, ready for a fertilised egg.

If the egg is fertilised, this equals pregnancy. However, if not fertilised, there is a drop in both oestrogen and progesterone and the uterus lining breaks down, which causes a period.

Then the process starts again! 

Women take hormonal contraceptives for a variety of reasons. There are different types, including hormonal and non-hormonal, and only hormonal contraceptives affect hormones and function based on synthetic hormones being released in the body.

This creates a very different response, preventing ovulation or build-up of the uterus lining to avoid pregnancy.

There is no change in FSH or LH: the synthetic hormones inhibit the production of FSH and prevent egg cells from maturing.

This graph highlights a combined pill containing the synthetic hormones oestradiol and progestin taken for 21 days with a 7-day break. At this point, the absence of synthetic hormones can result in premenstrual symptoms.

However, females may experience bleeding. This is not a period but is known as a withdraw bleed. Progestin hormones frequently prevent bleeding when taken continually, and when ovulation occurs the control of progesterone prevents the build-up of the uterus lining to allow for a fertilised egg to implant. Lower levels of progestin exist in comparison to a combined pill.