The Rhythm Within: Understanding the Menstrual Cycle Before Talking About PCOS

Why do I begin here?

I decided to start the CCL women's health series with the menstrual cycle. It is the most talked-about topic, yet still, it is the least clearly understood.

Every month, millions of women experience it. It shapes energy levels, emotions, fertility, and even metabolism, yet most of us grow up learning only

the surface details. In medicine, we call the body's normal ways of working "physiology," but in real life, it is a rhythm that influences how women work, rest, and live.

To understand conditions like polycystic ovary syndrome (PCOS), endometriosis, or amenorrhea, we first need to understand what the body is trying to do when everything is working in sync. Once we grasp the normal pattern, the deviations begin to make sense, and compassion deepens for those whose cycles bring discomfort, pain, or unpredictability.

So let's begin with what is considered normal in medicine, and the quiet choreography that happens inside women's bodies every month.

The body's monthly conversation

Unlike the male reproductive system, the female reproductive system follows a monthly rhythm.

It is a conversation between three key organs:

• the brain,

• the ovaries, and

• the uterus.

Every cycle begins when the brain's hypothalamus sends tiny bursts of hormone messages (GnRH) to the pituitary gland, which responds by releasing two hormones: FSH (follicle-stimulating hormone) and LH (luteinising hormone).

These two travel through the bloodstream to the ovaries, where dozens of small follicles, each holding an immature egg, begin to wake up and grow.

The follicular phase: Preparing for the possibility

This first part of the cycle begins on Day 1 — the first day of bleeding.

While the uterus sheds its old lining, one follicle in the ovary slowly becomes "dominant." It produces estrogen, which helps rebuild the uterine lining (the endometrium), making it thick, soft, and ready to welcome a new life if pregnancy happens.

Under estrogen's influence, even the cervical mucus changes. It becomes clearer and more slippery, allowing sperm to swim through more easily.

This "follicular phase" lasts until about Day 14 in an average 28-day cycle, but it can vary widely between women.

Ovulation: The main event

When estrogen levels peak, something remarkable happens. The body switches from "slow and steady" to "go now."

High estrogen tells the brain to release a surge of LH, which causes the dominant follicle to burst open and release an egg.

This phase is ovulation, the midpoint of the cycle.

Some women feel a twinge or slight pain when it happens; others notice changes in mucus or temperature.

After being released, the egg starts its path through the fallopian tube, where it might encounter sperm.

The luteal phase: Preparing for either outcome

After ovulation, the empty follicle transforms into a small hormone factory called the corpus luteum.

It starts releasing progesterone, the hormone of calm and preparation.

Progesterone makes the endometrium thicker and richer so that it is ready to nourish a fertilised egg.

It also changes the cervical mucus again, making it thicker to block sperm entry, and slightly raises body temperature (which is why some women track basal temperature for fertility awareness).

If pregnancy occurs, the embryo secretes hCG, which maintains the corpus luteum.

If not, progesterone and estrogen levels fall — signalling that it's time for the lining to shed.

Menstruation: The renewal phase

When those hormones drop, the uterine lining, no longer supported, breaks down and leaves the body as menstrual bleeding.

This phase is what we call a "period."

The fluid contains blood, mucus, and endometrial tissue, but usually no clots unless the flow is heavy.

Normal bleeding lasts up to 8 days.

The cycle then resets, beginning again with Day 1 of a new period.

When the rhythm shifts

Sometimes ovulation does not occur, which is called an anovulatory cycle.

Without ovulation, there is no progesterone rise, and the endometrium keeps growing under the influence of estrogen until it breaks down irregularly.

This kind of shift in the body's rhythm can lead to unpredictable bleeding, sometimes light, sometimes heavy, sometimes absent for weeks.

Conditions like PCOS, thyroid problems, or high prolactin can interfere with this normal rhythm.

That is why understanding this system matters, not only for fertility but also for mood, metabolism, and long-term health.

More than a monthly event

Doctors now describe menstruation as a "vital sign" because it is as important as heart rate or blood pressure.

Irregular or absent cycles can be early clues to hormonal, metabolic, or structural conditions that deserve attention.

For women, the menstrual cycle isn't just a biological clock — it's a mirror of overall health.

Key takeaways

• The menstrual cycle is a finely tuned system between the brain, ovaries, and uterus.

• Hormones like FSH, LH, estrogen, and progesterone work in feedback loops to prepare the body for pregnancy.

• Normal cycles last 24–38 days, with bleeding up to 8 days.

• Irregular or absent periods may signal hormonal imbalance, thyroid disease, or PCOS.

• Understanding the normal (physiological) pattern helps us recognise and manage when things go off balance.

Figure 1. Hormonal changes in normal menstruation versus PCOS. PCOS: Polycystic ovarian syndrome (Source: Chouhan & Garg, 2023, p. 47)

References

1. Thiyagarajan, D. K., Basit, H., & Jeanmonod, R. (2024). Physiology, Menstrual Cycle. In StatPearls. StatPearls Publishing.

2. American Academy of Pediatrics Committee on Adolescence, American College of Obstetricians and Gynecologists Committee on Adolescent Health Care, Diaz, A., Laufer, M. R., & Breech, L. L. (2006). Menstruation in girls and adolescents: using the menstrual cycle as a vital sign. Pediatrics, 118(5), 2245–2250. https://doi.org/10.1542/peds.2006-2481

3. Chouhan, P., & Garg, A. (2023). Ovulation induction in polycystic ovarian syndrome: A review of contemporary approaches. Journal of Medical Society, 37, 45-50. https://doi.org/10.4103/jms.jms_21_22