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The PCOS Newsletter is a weekly publication answering one PCOS question at the time so we can be empowered by knowledge.

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PCOS and Irregular periods

Updated: Feb 6, 2023

Hi, This is Francesca from The PCOS Newsletter where we provide answers to complex PCOS questions in a concise and easy-to-understand format. In today’s newsletter we are discussing irregular periods 🩸.

This week's question

Why do I have irregular periods?

The answer

When it comes to irregular periods (the symptom of PCOS I had to deal with my whole life), it is important to revise our reproductive cycle. If you already know how the menstrual cycle works, feel free to jump to: What happens in women with PCOS?

Us, women have an incredible monthly hormonal cycle. We are subject to variations in our hormones day by day. This offers us the amazing ability to create life. I will forever be in awe about what our bodies are able to do.

Let’s revise the menstrual cycle

The menstrual cycle is the series of changes that happen in a woman's body in preparation for pregnancy (our bodies are designed to create life on a monthly basis 🤯). It typically lasts about 28 days, but can range from 21 to 35 days. The menstrual cycle is controlled by hormones produced by the hypothalamus , the pituitary gland, and the ovaries 🧠.

An irregular period (officially called oligomenorrhoea) is defined as cycle length greater than 35 days.

The menstrual cycle is divided into two phases: the follicular phase and the luteal phase with ovulation 🎉 in the middle.

  1. 📈 The Follicular Phase: This phase begins on the first day of menstruation and lasts for about 14 days. During this phase, the lining of the uterus (endometrium) thickens, and the pituitary gland releases follicle-stimulating hormone (FSH). FSH stimulates the growth of a group of immature eggs (follicles) in the ovary. One of these follicles will eventually become the dominant follicle and continue to grow. As the dominant follicle grows, it produces increasing amounts of estrogen.

  2. 🎉 Ovulation: The rising levels of estrogen in the body cause the pituitary gland to release higher amounts of luteinizing hormone (LH). This surge of LH causes the dominant follicle to ovulate and release its egg. This process is called ovulation and it typically occurs around day 14 of a 28-day menstrual cycle.

  3. 🤗 The Luteal Phase: This phase begins after ovulation and lasts for about 14 days. After ovulation, the empty follicle (now called corpus luteum) produces progesterone and small amounts of estrogen. Progesterone helps to thicken the lining of the uterus in preparation for pregnancy. If pregnancy does not occur, the corpus luteum disintegrates and progesterone and estrogen levels drop. This causes the lining of the uterus to shed, resulting in menstruation, and starting a new menstrual cycle 🙌🏼.

What happens in women with PCOS?

PCOS can affect the whole menstrual cycle, however irregularities in hormones within the first part of the cycle can lead to failure to ovulate and as a result, irregular periods.

The main culprit is an increase in androgens which destabilises this perfectly oiled machine 🤖 before ovulation.

Ok, so what do these androgens do?

This is one of the questions that got me the most confused about PCOS. No one really talks about Testosterone when it comes to the hormonal cycle. However, it is always present. This is because estrogen, which is a hormone commonly associated with the menstrual cycle, actually starts as a series of androgens that are converted to estrogen as the follicle develops.

In a normal functioning cycle 🩸, as FSH pulsates throughout the follicular phase so does LH, but in smaller dosages compared to the ovulation stage 🎉. However in women with PCOS some things happen:

  1. Is is thought that the cells of the ovaries are over responsive to the action of LH leading to the over production of androgens (such as testosterone)

  2. Not only the ovaries my be over responsive, LH:FSH ratios are higher in women with PCOS meaning we may produce more LH which leads again to overproduction of androgens.

  3. Higher levels of insulin can also overstimulate the conversion of androgens in a more powerful testosterone form (although this theory is still under consideration).

This excess of androgens leads to an imbalance in estrogen levels and a failure to ovulate together with some of its other lovely symptoms: acne and hirsutism. The immature follicles that do not release eggs for ovulation can form into small cysts on the ovaries which is what they see in scans.

It's important to note that these theories are still being studied and could further developed in the future.

However, these are generalisations of the condition and can vary from person to person. This is why is extremely important to get to know your body and listen to signs of these mechanisms. With knowing comes clarity on next steps, so I would encourage you to keep track of what your are feeling throughout your cycle and get a healthcare professional to help you understand the ins and outs of your body.

I hope this helped bring some light onto this subject. Please don’t hesitate to reply to this email, leave a comment or submit your questions here, so we can explore them in further detail as we go along.

See you next Sunday!

Francesca ❤️


Hill, M. (2019). Period power: Harness your hormones and get your cycle working for you. Green Tree.

Witchel, S. F., Oberfield, S. E., & Peña, A. S. (2019). Polycystic ovary syndrome: Pathophysiology, presentation, and treatment with emphasis on adolescent girls. Journal of the Endocrine Society, 3(8), 1545–1573.

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