Progesterone is a hormone that is produced by both men and women. For men, it can help with sperm production, however, it’s known primarily as a female sex hormone because of the important role it plays in the female reproductive system and the menstrual cycle.

Read on to find out more about what progesterone is responsible for, where it is produced in the female body and when its production peaks.


What does progesterone do in the menstrual cycle?

Progesterone serves a number of functions, but predominantly, it’s there to get your body ready for pregnancy. When an egg is released by an ovary, progesterone encourages the thickening of the uterine lining, ready for a fertilised egg to implant into. However, if an egg isn’t fertilised, it is this lining that sheds during your period. The hormone can also help to keep your cycles more regular, making it easier to determine when your period is due to start.  

Progesterone is also important for conception and in the early stages of pregnancy. Too little progesterone, and couples may find it hard to conceive or may struggle to bring a baby to full term, suffering increased miscarriages compared to women who have higher levels of the hormone.  


Where is progesterone produced?

In women, progesterone is mainly produced in the ovaries, while in men, it is made in the adrenal glands.

The menstrual cycle is split into four main phases: menstruation, the follicular phase, ovulation and the luteal phase. During the follicular phase, a woman’s ovaries will produce between five and 20 ovarian follicles. The follicles are small sacs, and each sac contains an immature egg. Out of all of these follicles, typically only one egg matures enough to be released by an ovary, and the remaining immature eggs are reabsorbed into the body.


When does progesterone peak?

A woman’s progesterone levels peak right after an ovary releases a mature egg.  This is known as the luteal phase of the menstrual cycle and usually occurs around two weeks after the first day of your most recent period.

It peaks at this time because your body is preparing for a potential pregnancy. Once the egg has been released, it could get fertilised by sperm to begin the creation of a foetus. To prepare for this, your progesterone levels increase to help thicken the lining of the uterus.  

Should a pregnancy occur, progesterone levels will remain high as this helps to support the baby and ensure it survives and goes to term. In fact, it’s usually this hormone that’s responsible for the nausea and morning sickness that many women face in the first trimester of pregnancy.  Once the placenta is fully developed (usually after around 10 weeks), it takes over progesterone production and helps to support your baby.  

Progesterone levels are measured in nanograms per millilitre (ng/mL). Prior to ovulation, at the start of the menstrual cycle, this hormone measures less than 1 ng/mL. During and just after ovulation, it increases to around 12 ng/mL and in the first trimester of pregnancy, can rise to as much as 40 ng/mL.  Should a pregnancy not be achieved, the levels drop back to around 1 to 2 ng/mL, and the cycle begins again.


Can you have too much or too little progesterone?

You can produce too little progesterone, and may feel the side effects of this, however, too much progesterone doesn’t usually pose a problem.  

If your progesterone levels are too low, you might experience irregular periods, mood changes, anxiety and depression and headaches. It can also result in abnormal uterine bleeding.  

There are very few risks or symptoms associated with high progesterone.  In fact, some women do have higher levels of this hormone in their body thanks to some contraceptives, such as the progestogen-only pill. Progestogen is a synthetic version of progesterone, and the contraception works by preventing ovulation to reduce the chance of pregnancy by up to 99%.  



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