09/04/2010 11:37 BST | Updated 22/05/2015 06:12 BST

O: What Is Oestrogen?

Oestrogen is the name given to a group of hormones produced by a woman's ovaries.

This group - comprising oestradiol, oestrone, is responsible for regulating the woman's reproductive cycle; as well as maturing the female body for fertility by causing the breasts to grow and the menstrual cycle to commence.

During the menstrual cycle, oestrogen is responsible for causing the lining of the womb to thicken in order to accept and nourish a fertilised egg. Once pregnancy is established, oestrogen will also be created by the newly formed placenta (at around 10 weeks of pregnancy) in order to maintain the body's ability to carry the pregnancy.

Oestrogen continues to perform a function once a woman has given birth by suppressing the menstrual cycle of a breastfeeding mother. During this time, the oestrogen levels will be low which prevents ovulation from occurring. This is the body's way of ensuring that the woman's newborn is receiving maximum nourishment from its mother.

As well as a role in reproduction, oestrogen is also believed to maintain healthy bones, balance cholesterol and promote good skin.

Once a woman reaches the menopause, her levels of oestrogen will decline, leading to a range of symptoms including a decrease in bone density, vaginal dryness, hot flushes and fatigue.

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