Progesterone and Oestrogen

Progesterone and oestrogen are what are often referred to as 'female hormones'. They are critical to women's health. They not only control the menstrual cycle and a woman's ability to conceive and carry a child, but they also have a wider impact throughout the female body. It is important to understand how these hormones work, particularly if you're considering hormone-based contraceptives or hormone replacement therapies (HRT) for menopause.

Oestrogen and progesterone are secreted primarily by the ovaries. Men also have oestrogen, but in much smaller levels than females.

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What is the function of oestrogen?

Most of the oestrogen produced in a woman's body is produced by the ovaries. The adrenal glands above the kidneys and some fat tissues also produce small amounts of the hormone. Oestrogen is responsible for the secondary physical sex features in women. During puberty, the release of oestrogen in a young girl is responsible for the growth of breasts, the development of pubic and underarm hair and it triggers the start of menstrual cycles.

There are three different types of oestrogen produced by the body:

  • Estradiol: this is the most common type of oestrogen produced for women who're within childbearing age. This regulates the menstrual cycle and has other effects throughout the body
  • Estriol: this is the primary type of oestrogen produced during pregnancy
  • Estrone: This is the only type of oestrogen that is produced after menopause, once a woman's monthly menstruation stops

What Progesterone does

Progesterone is secreted from within the ovaries, from what is known as the corpus luteum. This is a temporary structure/gland that is produced after ovulation.

Progesterone's primary function is to prepare the endometrium (lining of the womb) for pregnancy after ovulation, thickening the lining to accept a fertilised egg. It also stops muscle contractions in the uterus, which could cause the egg to be rejected and expelled. If conception occurs, progesterone will continue to stimulate the body to stop further ovulation, and develop the blood vessels in the endometrium to provide the baby with nourishment.

Once the placenta develops, it will also start to excrete Progesterone, to supplement the hormones being excreted by the corpus luteum. As well as causing the body to change to support a pregnancy, it also helps prepare the breasts to produce milk.

Function in the menstrual cycle

The menstrual cycle is controlled by the levels of these two critical hormones – oestrogen and progesterone. The menstrual cycle describes the process a woman's body goes through on a monthly basis in preparation for pregnancy.

The start of the menstrual cycle is the first day of a woman's period, and the end is marked by the last day before their next period. The NHS state that the average length of a menstrual cycle is 28 days. However, this can vary from woman to woman, and cycles from 24 to 35 days long are all considered normal.

Oestrogen levels start to increase at the beginning of the menstrual cycle, building to a peak level mid-cycle (approximately day 14) when ovulation occurs and an egg is released. After this point levels of oestrogen begin to drop off and progesterone gets released to prepare the body for pregnancy.

If pregnancy does not occur, the levels of progesterone will begin to decrease and the corpus luteum will break down. This drop in progesterone levels sparks menstruation when the body sheds the lining of the uterus. The process will then repeat, with oestrogen levels again beginning to rise as the next cycle begins.

Physiological effects of oestrogen

Aside from controlling your menstrual cycle, oestrogen has other functions throughout the body:

  • It keeps cholesterol in control
  • It protects your bones and keeps them strong and healthy
  • It affects your brain, including your mood

What happens if you produce too little oestrogen?

If your oestrogen levels are too low, you may experience symptoms such as;

  • Periods becoming less regular or stopping altogether
  • Difficulty getting pregnant
  • Hot flushes or night sweats
  • Trouble sleeping
  • Dryness and thinning of the vagina
  • Mood swings
  • Dry skin

What happens if you produce too little progesterone?

If you produce too little Progesterone, you may have difficulty conceiving or carrying a child to term, as insufficient production will prevent the body making the necessary changes for pregnancy. If you do become pregnant, you'll be at a higher risk of miscarriage or pre-term labour.

Symptoms of low progesterone include:
  • Irregular and missed periods
  • Spotting or other abnormal uterine bleeding
  • Abdominal pain during pregnancy
  • Frequent miscarriages

Another implication of producing too little progesterone is that it can cause the level of oestrogen produced to be too high.

What happens if you produce too much oestrogen?

If you are producing too much oestrogen, you may experience symptoms such as:

  • Gaining excess weight around the hips, waist and thighs
  • Changes to your menstrual cycle including heavier or lighter bleeding
  • Increased symptoms of pre-Menstrual syndrome (PMS)
  • Fibrocystic breasts (non-cancerous lumps)
  • Fibroids in the uterus (non-cancerous tumours)
  • Fatigue and loss of sex drive

Hormone-based contraceptive medication can alter the amount of oestrogen and/or progesterone in the body, a common option for women looking to avoid pregnancy and alleviate various pre-menstrual symptoms such as heavy period, acne, stomach pains, polycystic ovary syndrome. Alternatively, hormone replacement therapy medication provides the possibility to improve the levels of oestrogen, progesterone or both hormones, which can help to lessen the symptoms associated withe menopause.

You can find out more about the contraceptive options available and the hormone replacement therapy options available here.