Reviewed October 2019

Polycystic ovary syndrome and why you might have irregular periods

PCOS and irregular periods

There are a great many reasons why someone may have irregular periods, with the most common causes being pregnancy, low or high body weight, emotional stress, thyroid disorders, and polycystic ovarian syndrome (PCOS). Some less common causes of irregular periods include high prolactin levels from benign tumours, premature menopause, endometrial adhesions as a result of gynaecological procedures, and conditions causing excess testosterone levels. If your periods become irregular after previously being regular it is important to go and get checked out at the doctors to rule out anything serious.

PCOS is common, and can have a big effect on your menstrual cycle, so it is likely you will be tested for it if you do see your GP about irregular periods. But how exactly does it affect your periods, and what is the solution?

PCOS is a term that is bandied about quite a bit, but unless you have already been diagnosed with the condition it is unlikely you would know that much about it, even if you know someone who has it. In fact, the condition is estimated to affect between 2-26% of women, and may differ according to ethnic background.1 The Royal College of Obstetricians and Gynaecologists advises a diagnosis of PCOS using the Rotterdam Criteria,2 which states that you have PCOS if you have two out of the following three things: excess male hormones (hyperandrogenism, which is high levels of testosterone in the blood that may result in facial hair or acne), irregular periods or ovulation (less than six to nine periods per year), or polycystic ovaries on ultrasound (12 or more small follicles in one or both ovaries, or an ovary larger than 10cm, cubed).3

Why does PCOS cause irregular periods?

The how and why of irregular periods and PCOS relate to the finely-tuned dance between all the hormones that play a part in our menstrual cycle. The combined purpose of all these interactions is to mature an egg each month, release it in anticipation of fertilisation, and prepare the womb to potentially receive a fertilised egg to nurture and grow into a baby. When this doesn’t occur, the womb lining (endometrium) is shed.

Follicular stimulating hormone (FSH) and luteinising hormone (LH) are released from the pituitary gland, a small gland in the middle of the brain. FSH stimulates the growth of follicles (small, fluid-filled cavities) in the ovary. Each follicle contains an immature egg to be nurtured. As they grow, the follicles produce oestrogen, which thickens the lining of the womb. The rise in oestrogen levels also causes a sharp increase in luteinising hormone, which triggers the release of a mature egg (ovulation), and supports the remains of the follicle that delivered this egg. This “retired” follicle then produces its own set of hormones, namely progesterone. Progesterone is needed to establish and keep a pregnancy going in its very early stages, and as such it also promotes the thickening of the lining of the womb. If the egg isn’t fertilised, both oestrogen and progesterone hormone levels drop, which signals the lining of the womb to shed.

Given that each hormone is dependant on the others to do what it has to do, it’s not surprising that small changes or upsets can have a knock-on effect that throws everything off balance. In people who have PCOS there is no surge of LH to precipitate ovulation, although no one knows why this is, and women with PCOS have a higher baseline level of LH, again for reasons unknown.4 In addition, the body (stroma) of the ovary may produce an excess of male hormones to further stifle the process. As a result, many follicles form (poly cysts) but none grow and mature enough to release an egg (ovulate). The hormonal imbalance also means that there is no natural rise and fall of oestrogen and progesterone stimulating the lining of the womb to thicken and then shed.

But where do these male hormones come from? As it turns out, ovaries naturally produce low levels of testosterone which makes up the hormonal balance of women. In fact, the same building blocks that make testosterone also make oestrogen. When LH levels are raised in PCOS, testosterone production in the ovary is increased.5 To complicate matters further, high levels of insulin in the blood stream also result in higher free testosterone levels, which throws off the hormonal balance further. In fact, insulin resistance occurs when, for a variety of reasons, the cells of your body don’t let insulin in as easily. While insulin resistance doesn’t cause PCOS, the two conditions are related.

So, if you do end up being diagnosed with PCOS, what can you do about it? And is it important to regulate your periods, or does it not matter? These questions can be tackled by looking at the four issues associated with PCOS: irregular menstruation, ovulation, insulin resistance, and hyperandrogenism.

How can you regulate periods if you have PCOS?

It’s advisable to shed your endometrial lining at least once every 3-4 months, so that there isn’t a risk of developing endometrial hyperplasia (a build-up of the lining of cells of the womb).6 The significance of this is questionable and studies are still being done, but a very rare extrapolation (prediction) suggests that this predisposes you to endometrial cancer.7 Regulating your cycle can be accomplished by losing weight to normalise your menstrual cycle as fat secretes hormones including oestrogen, affecting your overall hormone balance. Decreasing this extraneous source of hormones leads to a more regulated cycle. Going on the pill to ensure you bleed every month, or taking hormone tablets once every 3-4 months can both also help regulate the menstrual cycle.

Weight loss can also help to regulate ovulation if you are trying to conceive. Your fertility expert may offer you a keyhole surgery called “ovarian drilling” that essentially pokes holes in the body of the ovary in an effort to decrease the tissue producing testosterone.

Diet and exercise help to regulate insulin resistance, with weight loss being the single most helpful change you can make. This isn’t always easy with insulin resistance however, so it can initially feel like a vicious circle, as essentially being insulin resistant encourages the body to store fat. This is because the cells of the body don’t let insulin in as easily, so blood glucose levels remain higher for longer, as do circulating insulin levels. This makes the body go into extra storage mode as a result of having ‘too much sugar’. Having PCOS and insulin resistance can predispose you to developing diabetes in pregnancy and later in life,8 so as you get older your doctor will screen you for signs that you are developing this condition.

Lastly, you can seek treatments for the signs of hyperandrogenism (excess male hormones). Cosmetic measures such as waxing, laser hair removal, electrolysis, or creams that have eflornithine (which incidentally is also used to treat African sleeping sickness) may work to remove excess hairs brought on by increased androgen levels (hirsutism). What is most important is how you feel: if this hair growth isn’t a problem for you, there is no clinical need to remove it. But there is nothing to be ashamed of or worried about if you’d like to remove it, either.

If you are experiencing irregular periods, it is important to seek help and advice from your doctor, who will be able to test you for conditions including PCOS and provide you with treatment.

Last updated October 2019
Next update due 2022

Disclaimer: This content is designed to provide general information and is not a substitute for medical advice. Medical opinion, practice and routine may vary from country to country and may change from time to time. The author is not liable for the results of misuse or inappropriate application of the information. If you are an individual who chooses to access this information, you should not rely on the information as professional medical advice or use it to replace any relationship with your doctor or other qualified healthcare or social care professional. For medical concerns, including decisions about medications and other treatments, individuals should always consult their doctor or, in serious cases, seek immediate assistance from emergency personnel. Individuals with any type of medical condition are specifically cautioned to seek professional medical advice before beginning any sort of health treatment. Individuals with specific queries or concerns should seek appropriately qualified medical advice. Clinicians must use their own judgement when interpreting this information and deciding how best to apply it to the treatment of patients.

Dr. Natasha Abdul Aziz, MBBCh BAO (NUI) LRCP&SI MRCOG

Natasha is senior clinical fellow in Obstetrics & Gynaecology with the Chelsea & Westminster NHS foundation trust. She was previously a clinical research fellow at the University of Oxford and national women’s health lead for the Muslim Doctors Association of the UK. Her special interests include the use of digital healthcare solutions to help vulnerable populations of women, volunteer work with refugees, and chasing that last sliver of sun on her balcony after work.

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  1. NICE, ‘Polycystic ovary syndrome,’ Clinical Knowledge Summary, National Institute of Health and Care Excellence, September 2018, [online],!backgroundSub:2 (accessed 27 October 2019)
  2. RCOG, ‘Long-term Consequences of Polycystic Ovary Syndrome’, Green-top Guideline, no. 33, 2014, [online],, (accessed 27 October 2019)
  3. NICE, ‘Polycystic ovary syndrome,’ Clinical Knowledge Summary, National Institute of Health and Care Excellence, September 2018, [online],!diagnosisSub:1 (accessed 27 October 2019)
  4. Tsilchorozidou, T., et al., The pathophysiology of polycystic ovary syndrome, Clinical Endocrinology, 2004, vol 60, pp 1-17
  5. Ibid.
  6. RCOG, ‘Long-term Consequences of Polycystic Ovary Syndrome’, Green-top Guideline, no. 33, 2014, [online],, (accessed 27 October 2019)
  7. Ibid.
  8. Ibid.

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