5 Things you might not know about your menstrual cycle

Think You Know Your Period? Think Again.

By Dr Fran Yarlett, NHS GP, Clinical Advisor at Phase.  

Most women were taught about menstruation, but not about the full complexity of their menstrual cycle. The truth? You don’t just have a period - you have a whole hormonal ecosystem. And understanding it could change the way you work, eat, move, and live.

1. A typical menstrual cycle is not 28 days long

Despite the myth of the "perfect" 28-day cycle, most women don’t have a textbook 28‑day cycle. A healthy adult cycle can range from 21 to 35 days - and a study of 1.6 million menstrual cycles confirms 91% fall in that range, while only around 16% have a 28‑day median. (1)

But even more importantly, your menstrual cycle isn’t just a reproductive rhythm -  it’s a vital sign. Fluctuations in your cycle can be one of the first indicators of stress, undernourishment or medical problems such as thyroid disorders.

2. Your period isn’t just blood 

During menstruation, the average woman loses about 30–80 ml of fluid - that’s 2 to 6 tablespoons over 3–7 days. More than 80 ml may be classified as heavy menstrual bleeding (HMB),  which is not normal, and you should see a healthcare professional to rule out underlying issues.(2)

But what’s being shed isn’t just blood. Period fluid includes the uterine (womb) lining, cervical mucus, and vaginal secretions, which is why a period’s consistency, colour and texture can change from day to day. (3)

3. Some women experience ovulation pain and mistake it for something else

Called mittelschmerz, (German to literally mean “middle pain”) this is a sharp, short-lived pain felt on one side of the lower abdomen during ovulation, usually around the middle of your cycle. Many women mistake it for gastrointestinal issues or early PMS, not realising it's a normal (if sometimes uncomfortable) ovulatory signal. (4)

4. Your physiology changes throughout your cycle

Your hormonal cycle doesn't just impact your mood - it affects your body  in measurable ways. For example:

1. You're strongest and most pain-tolerant around ovulation
   In the days leading up to and just after ovulation, estrogen peaks, boosting strength, coordination, and pain threshold. (5, 6)

2. Your metabolism speeds up in the luteal phase
   After ovulation, during the luteal phase, your resting energy expenditure can increase by 90–280 calories per day. This is why cravings and hunger often ramp up -  your body actually needs more fuel. (7)

3. Your cycle can change how your voice sounds

Subtle shifts in vocal cord tissue during your cycle — particularly around ovulation — may alter tone, pitch, or vocal fatigue, especially in singers or people who use their voice professionally. (8)

5. Even your brain changes through the cycle

Recent neuroimaging studies show that the structure of your brain shifts across the cycle, especially in areas linked to memory and learning, like the hippocampus. These changes are influenced by rising and falling estrogen levels. (9)

What does that mean in practice? Your energy, focus, memory, and creativity will likely fluctuate across the month, and that’s not a flaw. That’s your biology.

Phase can help you work with your cycle - not against it

Phase helps women and people with cycles understand these shifts, so that they can work with their changing strengths, rather than against them.  With Phase, you’ll get clear insights on when to push, when to pause, and how to align your workflow with your biology - not despite it. Learn more about your cycle by visiting our blog.

References

1. Grieger JA, Norman RJ. Menstrual Cycle Length and Patterns in a Global Cohort of Women Using a Mobile Phone App: Retrospective Cohort Study. J Med Internet Res. 2020 Jun 24;22(6):e17109. doi: 10.2196/17109. PMID: 32442161; PMCID: PMC7381001.

2. Fraser IS, Critchley HO, Broder M, Munro MG. The FIGO recommendations on terminologies and definitions for normal and abnormal uterine bleeding. Semin Reprod Med. 2011 Sep;29(5):383-90.

3. Thiyagarajan DK, Basit H, Jeanmonod R. Physiology, Menstrual Cycle. [Updated 2024 Sep 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-.

4. Cleveland Clinic: https://my.clevelandclinic.org/health/diseases/9134-ovulation-pain-mittelschmerz

5. Hellström B, Anderberg UM. Pain perception across the menstrual cycle phases in women with chronic pain. Percept Mot Skills. 2003 Feb;96(1):201-11. doi: 10.2466/pms.2003.96.1.201. PMID: 12705527.

6. https://www.sciencedirect.com/science/article/pii/S1526590012004774?utm_source=chatgpt.com

7. Jessica A L Tucker, Seth F McCarthy, Derek P D Bornath, Jenna S Khoja, Tom J Hazell, The Effect of the Menstrual Cycle on Energy Intake: A Systematic Review and Meta-analysis, Nutrition Reviews, Volume 83, Issue 3, March 2025, Pages e866–e876, https://doi.org/10.1093/nutrit/nuae093

8. Zamponi V, Mazzilli R, Mazzilli F, Fantini M. Effect of sex hormones on human voice physiology: from childhood to senescence. Hormones (Athens). 2021 Dec;20(4):691-696. doi: 10.1007/s42000-021-00298-y. Epub 2021 May 28. PMID: 34046877; PMCID: PMC8594207

9. Barth C, Steele CJ, Mueller K, Rekkas VP, Arélin K, Pampel A, Burmann I, Kratzsch J, Villringer A, Sacher J. In-vivo Dynamics of the Human Hippocampus across the Menstrual Cycle. Sci Rep. 2016 Oct 7;6:32833. doi: 10.1038/srep32833. PMID: 27713470; PMCID: PMC5054394.

Photo by Annika Gordon on Unsplash