Everything you need to know about the ovaries

The ovaries hold the key to female fertility and reproduction by producing eggs and the main female sex hormones.

In this article, we explore the function of the ovaries, and the impact hormonal imbalances can have on women’s health.

We cover:

• What are the ovaries and what do they do?
• What hormones do the ovaries make?
• What does oestrogen do in women?
• What does progesterone do in women?
• Why is testosterone important for women?
• What can affect ovarian hormones?
• The ovaries and menopause
• What health conditions can affect the ovaries?
• How to check your hormones

What are the ovaries and what do they do?
 

The ovaries are two small, oval-shaped organs that sit on either side of your uterus. They’re the primary female reproductive organs (or female gonads)—the equivalent of the testes in men.

The ovaries are also endocrine glands. They produce and secrete hormones that control many functions and processes in your body, including the physical changes that happen at puberty and your menstrual cycle.

 

The ovaries have two main reproductive functions in women:

1. Egg production

The ovaries make and store female reproductive cells (or gametes), known as ova or egg cells.

A woman is born with a lifetime supply of around one million egg cells in her ovaries. From birth, the number of egg cells begins to decline, and, by puberty, only 25% of the egg supply remains [1].

Each egg cell (or ovum) is housed within a tiny sac called a follicle. During a woman’s reproductive years, an egg is usually released every 28 days in a process called ovulation. If the egg is fertilised by a sperm, pregnancy can happen.

Our Anti-Mullerian Hormone (AMH) Blood Test can give you an idea of your egg count (or ovarian reserve). Although it can’t tell you your exact number of eggs, it can give you an indication, based on the level of hormone released by the ovarian follicles. This can help in pregnancy planning.

2. Hormone production

The ovaries also make female sex hormones that play vital roles in regulating the menstrual cycle and supporting pregnancy.

Ovarian hormones are also important for women’s overall health and wellbeing. For instance, they’re involved in supporting bone and skin health.

 

What hormones do the ovaries make?
 

The ovaries make the two main female sex hormones:

• Oestrogen
• Progesterone

What does oestrogen do in women?
 

Oestrogen plays an important role in puberty, the menstrual cycle, pregnancy, and many other functions in the female body.

Functions of oestrogen in women include: 

• Controlling cholesterol levels to protect heart health
• Development of female secondary sex characteristics
• Preparing the lining of the uterus (endometrium) for pregnancy
• Brain function
• Maintaining bone density
• Regulating mood
• Regulating the menstrual cycle
• Supporting collagen levels in the skin
• Supporting sex drive

What are female secondary sex characteristics?

A female secondary sex characteristic is a physical trait that’s associated with the female sex. However, it’s not directly involved in reproduction. These characteristics start to develop when oestrogen levels rise at puberty.

In women, secondary sex characteristics include:

• Breast development
• Growth of pubic and underarm hair
• Widening of the hips

What does progesterone do in women?
 

Alongside oestrogen, progesterone helps regulate the menstrual cycle. It also helps prepare the female body for pregnancy and supports pregnancy as it progresses.

Functions of progesterone in pregnancy include:

• Maintaining the health of the placenta to nourish the baby
• Preventing preterm labour by stopping the uterus from contracting
• Supporting the growth of milk ducts in the breasts
• Thickening the lining of the uterus to prepare for implantation of a fertilised egg

Like oestrogen, progesterone has non-reproductive functions in women, including:

• Helping to maintain bone strength
• Promoting skin elasticity and firmness
• Protecting cardiovascular health

What are the four phases of the menstrual cycle?
 

The four phases of the menstrual cycle are governed by oestrogen, progesterone, and several other hormones. They prepare the body for pregnancy, and if pregnancy doesn’t happen, the cycle begins again.

The four phases of the menstrual cycle:

1. Menstrual phase (days 1–5*): this phase begins on the first day of your period. Low oestrogen and progesterone levels during this phase trigger the shedding of the uterine lining, resulting in menstruation.
2. Follicular phase (days 1-13): the pituitary gland releases follicle-stimulating hormone (FSH), which causes an egg to mature in the ovaries. As the egg develops in the follicle, the follicle begins to secrete oestrogen, which helps rebuild the uterine lining.
3. Ovulation phase (day 14): rising oestrogen levels trigger a surge of luteinising hormone (LH) from the pituitary. This causes the follicle to release a mature egg from the ovary. The egg travels through the fallopian tube, where it may be fertilised by a sperm.
4. Luteal phase (days 15–28): after ovulation, the empty follicle forms the corpus luteum—a collection of cells that forms on the ovary. The corpus luteum releases progesterone, which maintains the thickened uterine lining in preparation to receive a fertilised egg. If the egg is not fertilised, the corpus luteum and the uterine lining break down, and menstruation begins again.

If a fertilised egg implants in the uterus, hormone levels rise to support pregnancy. The corpus luteum makes progesterone for the first eight to 12 weeks of pregnancy, then the placenta takes over its production.

*These day numbers are given as a guide only. Periods can last from two to seven days, and it’s common for the menstrual cycle to range from 23 to 35 days [2].

Why is testosterone important for women?
 

Although it’s known as a male sex hormone, women also produce small amounts of testosterone, both in the ovaries and the adrenal glands.

In women, testosterone plays a role in:

• Bone health
• Breast health
• Fertility
• Sex drive

Both women and men produce many of the same hormones, but in different amounts. For example, men also make oestrogen in the testes—albeit in much smaller quantities than women.

What can affect ovarian hormones?
 

There are many reasons why ovarian hormones can become imbalanced—including diet and lifestyle choices, ageing, and medical conditions.

Causes of ovarian hormone imbalances include:

• Body weight—low body weight and obesity can both cause oestrogen imbalances that can affect the menstrual cycle and fertility.
• Menopause—as women approach menopause, ovarian hormones levels decline, which can cause wide-ranging symptoms like low libido and brain fog.
• Stress—chronic stress increases cortisol levels, which can affect oestrogen and progesterone. It can impact ovulation and cause periods to become irregular or temporarily stop (amenorrhea).
• Lifestyle choices—for example, smoking can disrupt hormone production.
• Exercise—overexercising can reduce oestrogen levels and cause irregular or absent periods.

What happens to the ovaries in menopause?
 

Menopause is a stage in a woman’s life when the ovaries stop releasing eggs, and oestrogen and progesterone levels decline significantly. It marks the end of the reproductive years and usually happens at around the age of 51 [3].

Women can experience symptoms in the transition to menopause (perimenopause) and post-menopause.

Common menopause symptoms include:

• Weight gain
• Low mood
• Sleep problems

For some women, these symptoms can be severe and affect their quality of life. Hormone replacement therapy (HRT) may be helpful in treating the symptoms of falling levels of ovarian hormones.

If you’re under 45 and experiencing symptoms of menopause, our Menopause Blood Test can help determine if you’re in early menopause.

It checks hormone levels including FSH, which is higher than normal in the transition to menopause, and oestradiol, which is lower than normal at this time.

Symptoms of menopause can be similar to those of other conditions, such as an underactive thyroid (hypothyroidism). A thyroid blood test can help distinguish between menopausal symptoms and a thyroid disorder.

What health conditions can affect the ovaries?
 

Several health conditions can affect the ovaries, impacting their function and potentially leading to problems with fertility.

Symptoms of ovary problems may include [4]:

• Irregular periods
• Nausea or diarrhoea
• Pelvic pain or bloating
• Period pain (dysmenorrhea)
• Vaginal discharge

Conditions that affect the ovaries include:

• Ovarian cysts—common growths that can form in or on the ovaries. They’re usually harmless and resolve without treatment.
• Pelvic inflammatory disease (PID)—an infection that can happen in the ovaries, fallopian tubes, or uterus. It’s typically caused by a sexually transmitted infection (STI). Prompt treatment, usually with antibiotics, helps prevent complications such as infertility.
• Polycystic ovary syndrome (PCOS)—a common condition that affects women’s ovaries and can make it difficult to get pregnant naturally. Although there’s no cure for PCOS, there are treatments that can help manage symptoms and avoid complications. There are also ways you can manage PCOS naturally.
• Premature ovarian insufficiency (POI) —a rare condition where a woman’s ovaries stop working before the age of 40, which can lead to infertility.
• Ovarian cancer—the abnormal growth of cells in the ovaries or fallopian tubes. It can be hard to detect as symptoms often don’t develop until the later stages.

How to check your hormones
 

If you have symptoms that you think may be hormone-related, or you just want to check your hormone levels are in healthy ranges, try our Female Hormone Blood Test.

If you’re not sure which test is right for you, check out our bestselling tests in our Female Hormone Blood Test Buying Guide.

We also have buying guides for our Fertility Blood Tests and Thyroid Blood Tests. And you can learn more about hormone health in our Hormone Health Hub.

 

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References

1. The Committee on Gynaecologic Practice of the American College of Obstetricians and Gynaecologists and The Practice Committee of the American Society for Reproductive Medicine (2008) Age-related fertility decline: a committee opinion. Fertility and Sterility, 90(3), 486-487 https://doi.org/10.1016/j.fertnstert.2008.08.006.
2. NHS Inform (2024) Menopause. Available at: https://www.nhsinform.scot/healthy-living/womens-health/later-years-around-50-years-and-over/menopause-and-post-menopause-health/menopause/ [Accessed 18 September 2024].
3. Cleveland Clinic (2022) Ovaries. Available at: https://my.clevelandclinic.org/health/body/22999-ovaries [Accessed 18 September 2024].
4. March, W., Moore, V., Willson, K., Phillips, D., Norman, R. and Davies, M. (2009) The prevalence of polycystic ovary syndrome in a community sample assessed under contrasting diagnostic criteria. Human Reproduction, 25(2), pp.544-551.