Oestrogen

Oestrogens are a group of hormones primarily responsible for the development of female sex organs and secondary sex characteristics. While oestrogen is one of the major female sex hormones, small amounts are found in males. In women, follicular stimulating hormone (FSH; produced by the pituitary gland) stimulates cells (follicles) surrounding the eggs in the ovaries, causing them to produce oestrogen. When the oestrogen levels reach a certain level, the hypothalamus produces luteinising hormone (LH), which eventually causes the release of the egg, beginning the preparation for fertilization.

There are three main oestrogen fractions: oestrone (E1), oestradiol (E2), and oestriol (E3).  

• Oestrone (E1) is the major oestrogen after the menopause. It is derived from chemicals released from the adrenal gland and is also made in adipose tissue (fat).
• Oestradiol (E2) is produced in women mainly in the ovary. In men, the testes and adrenal glands are the principal source of oestradiol. Normal levels of oestradiol provide for proper ovulation, conception, and pregnancy, in addition to promoting healthy bone structure and regulating cholesterol levels in females.
• Oestriol (E3) is the major oestrogen in pregnancy, with relatively large amounts produced in the placenta (from chemicals produced by the baby's adrenal glands and liver). Oestriol levels start to rise in the eighth week of pregnancy and continue to rise until shortly before delivery. Serum oestriol circulating in maternal blood is quickly removed from of the body by the kidneys. Each measurement of oestriol is a snapshot of what is happening with the placenta and fetus, but there is also natural daily variation in the oestriol level.

A blood sample will be drawn from a vein in your arm, or rarely you will be asked to provide a urine samples which may involve a 24-hour collection.