Fertility is the ability to produce offspring.

Continuous fertility

In men, fertility is continuous. Levels of testosterone, FSH and ICSE are kept relatively constant through negative feedback. As a result, sperm are produced continually.

Cyclical fertility

In women, fertility is cyclical. Levels of oestrogen, progesterone, FSH and LH fluctuate. As a result women are only fertile for a small number of days before and after ovulation during each menstrual cycle.