Life with Oura
Oura Crew | Jun 21, 2018

Understand and Track Your Menstrual Cycle Phases

The menstrual cycle impacts women’s life on a monthly basis. So how to track it and its effects? In this article, PhD Jana Podlipská from the Oura science team explains how the menstrual cycle affects women. She also shows how the data you’ll see in the Oura app and Oura Cloud reveals some of the effects.

Most women are familiar with this: at certain times of month, you feel physical discomfort, tiredness or moodiness. Sometimes words like cranky or irritated have even been used (many times leading to even increased crankiness and irritation, must add). It has to do with your menstrual cycle, of course.

But why is it so, why does the menstrual cycle affect women like that? The answer is quite simple: Every woman who goes through the cycle every month is experiencing a rollercoaster of hormonal fluctuations. The hormones have an impact on both your physiology and behavior.

The new Oura ring features body signal tracking that can help you monitor your menstrual cycle and see some of the ways it affects your body.

In this article you’ll learn:

The menstrual cycle and all physiological changes related to it are, of course, highly individual. Many issues ranging from the use of contraceptives to physiological conditions have an influence on the cycle, its effects, and how much you can track them.

The Menstrual Cycle Phases

Before digging deeper into the outcomes of the hormonal fluctuations women face, let’s revisit the basics of the menstrual cycle.

Menstrual cycle, hormone levels and body temperature deviation. Source: https://commons.wikimedia.org/wiki/File:MenstrualCycle2_en.svg

The menstrual cycle starts with the first day of menstruation and usually lasts from 21 to 35 days, the average duration being 28 days. The cycle can be divided into two main phases: pre-ovulatory (i.e. follicular) and post-ovulatory (i.e. luteal). Ovulation marks the midpoint of the cycle.

Monthly Hormonal Fluctuations

The pre- and post-ovulatory phases of the cycle are characterized by specific hormonal changes that affect the physiology of women’s bodies. [Ecochard 2015]. During the pre-ovulatory phase, the levels of a hormone called estrogen are gradually increasing. Together with follicle-stimulating hormone (FSH), estrogen prepares the woman’s body for possible pregnancy.

By the end of the pre-ovulatory phase, another player called luteinizing hormone (LH) surges and triggers ovulation. The ovulation day can be used as a benchmark for days with the highest probability of becoming pregnant. The fertility window span starts generally 3–5 days before the ovulation and ends on the ovulation day. [Ecochard 2015]

In the post-ovulation phase, a hormone called progesterone dominates the menstrual cycle. It rises to its maximum level mid post-ovulation phase. (In case you don’t get pregnant.)

The Effects of Monthly Hormonal Fluctuations

Physical discomfort and mood swings are very common for most women who go through the menstrual cycle. The cyclic hormonal fluctuations are the main reason why women are glowing on one week, and feel low, oversensitive, sad or angry on another.

At mid-cycle, just before the ovulation and when the estrogen hormone reaches its optimal amounts, women usually feel at their best. In studies, they’ve for example reported high levels of well-being and self-esteem [Farage 2008].

During the late post-ovulatory phase (about a week before menstruation), the fast decline in both estrogen and progesterone hormones starts to negatively manifest itself. This is the time when many women may experience tender or lumpy breasts, fluid retention, bloating, cramps, cravings, mood swings, tiredness or anxiety.

According to research, about 80% of women experience some of these symptoms up to some level. Based on the symptom severity, about 30% of women are diagnosed with premenstrual syndrome (PMS) and 3–8% suffer from premenstrual dysphoric disorder (PMDD).

How to Track the Menstrual Cycle Phases with Oura

So, how is this natural mechanism of menstrual cycle reflected in your body’s physiological changes? And how can you detect those changes with the Oura ring?

There are several body signals that the Oura ring tracks which can help you follow what happens in your body during the cycle:

A combination of these measures draws a picture about the current cycle phase, approximate cycle length, and the potential mood swings. Moreover, it may even help you to track your fertility. But bear in mind that fertility is such a complex topic that a lot of further research is needed before anything specific can be said about it, let alone make any prognoses.

Body Temperature Deviation

Body temperature is one of the core physiological players affected by estrogen and progesterone hormone fluctuations during the cycle. It has been shown that estrogen promotes the widening of blood vessels, heat dissipation and lower body temperatures. Conversely, progesterone promotes the narrowing of the blood vessels, heat conservation and higher body temperatures [Charkoudian 2017].

What this means in practice is that during the menstrual cycle, as the hormonal levels vary, body temperature varies as well. The body temperature increase in post-ovulation phase can be anything between 0.3–0.6°C in comparison to the pre-ovulation phase [Baker 2007, Shilaih 2017].

Each night, the Oura ring measures your peripheral body temperature and displays it as temperature deviation with reference to your temperature baseline. For most women with a menstrual cycle, the monthly body temperature variation has a biphasic shape/rhythm. Here’s how it looks like in the Oura app:

And here’s how the temperature trend looks like in Oura Cloud.

The graph illustrates the weekly temperature deviation of a woman with menstrual cycle length 28 days. Low peaks and areas under the temperature baseline (0.0 °C) correspond approximately to the pre-ovulation phase. High peaks and areas above the temperature baseline correspond approximately to the post-ovulation phase.

On a physiological level, the graph shows how in the pre-ovulation phase, when estrogen hormone is dominating, body temperature slightly decreases and reaches the lowest point around the ovulation time. After ovulation, when the progesterone levels increase, body temperature rises and peaks around the mid phase, dropping again towards the end of the cycle.

Resting Heart Rate, Heart Rate Variability, Respiratory Rate

The menstrual cycle affects also women’s cardiovascular system and respiratory rate. Several studies have indicated an increase in heart rate, decrease in heart rate variability and elevation of respiratory rate throughout the menstrual cycle [Tenan 2014, de Zambotti 2013, Brar 2015].

Why is that? First of all, your heart rate and respiratory rate are controlled by your autonomic nervous system. It, in turn, is linked to your hormonal fluctuations during the menstrual cycle [Brar 2015, Tenan 2014].

The autonomic nervous system has two branches: the stimulating sympathetic (also called as fight-or-flight), and the inhibiting parasympathetic (also called rest-and-digest). During the pre-ovulation phase, parasympathetic nervous activity usually increases. This leads to a calming effect on women’s physiological functions, and therefore lower heart rate, respiratory rate and higher heart rate variability.

Conversely, the sympathetic activity dominates later in the cycle, explaining the elevation in heart rate, respiratory rate and a decrease in heart rate variability. [Tenan 2014, de Zambotti 2013, Brar 2015].

The graph above nicely demonstrates the synchronization of resting heart rate (purple curve) with body temperature deviation (orange curve) across the menstrual cycle. Lower resting heart rate and body temperature occur during pre-ovulatory phase, whereas higher resting heart rate and body temperature occur during post-ovulatory phase.

This graph, on the other hand, shows the weekly average values of heart rate variability (purple curve) and body temperature deviation (orange curve). We can see that the heart rate variability behaves pretty much conversely to the body temperature. It has higher values during the pre-ovulatory phase when body temperature decreases and lower values during post-ovulatory phase when body temperature is higher.

The third graph shows weekly average values of nocturnal respiratory rate (purple curve) and body temperature deviation (orange curve). Respiratory rate follows the body temperature pattern across the menstrual cycle. Respiration is slower at the beginning of the cycle when temperature is low and speeds up towards the end of the cycle as temperature rises.

Hormonal Contraceptives

What if you’re using combined hormonal contraceptives? Exogenous hormones, i.e. oral contraceptives, keep both estrogen and progesterone elevated across the menstrual cycle and therefore the body temperature stays relatively stable in a long term [Baker 2001]. Absolutely, the temperature values are approximately equal to body temperature during the luteal phase [Baker 2001].


Similarly, the cardiac function seems to be unaffected by the oral contraceptives due to the constant dosage of female hormones resulting in low variation in HR and HRV across the cycle [Teixeira 2015].

How to Fight Off PMS?

One of the burning questions many women might have is how to fight off the not-so-pleasant symptoms of the hormonal fluctuations? There are luckily some ways to ease some of the discomfort.

Exercise

Exercise makes you happy. During physical activity, your body releases hormones called endorphins which boost your mind and make you feel good. Moreover, endorphins reduce pain perception, thus aiding to fight physical aches. Try yoga, walking, jogging, swimming or working in the garden. Anything you enjoy and that makes you smile!

Eat well, regularly, and in small portions

Following healthy eating habits, also while you are craving for sweets or other junk food, will pay off. Large meals and meals rich in carbohydrates cause blood sugar swings which may worsen the emotional instability.

To keep your blood sugar levels stabilized, try to choose a meal that has quality protein (such as fish, lean meat or legumes) with whole grain sides and plenty of veggies. Try also to stick with healthy snacks such as nuts or fruits. Too much salt or sodium, both common in processed foods, will exacerbate water retention and possible swelling. Also caffeinated drinks, such as coffee or energy drinks, may leave you feeling more anxious and stressed. Therefore, you might want to consider trying out herbal teas such as chamomile or lemon balm to soothe your nervous system.

Sleep well

Adults need in general between 7–9 hours of sleep per night. Make sure you get as much quality zzz as your body craves to keep your mood lifted and to leave anxiety, tiredness and irritation at the bay.

Do you want to know more about body temperature tracking with the Oura ring? Check out What can you learn from your body temperature trends article.

Sources:

https://www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186

https://www.menstrupedia.com/articles/physiology/cycle-phases

http://teachmephysiology.com/reproductive-system/development-maturation/menstrual-cycle/

https://www.avogel.co.uk/health/periods/symptoms/mood-swings/

https://en.wikipedia.org/wiki/Premenstrual_syndrome

Ecochard, R et al. Self-identification of the clinical fertile window and the ovulation period. Fertility and Sterility, 2015 May;103(5):1319-25.e3.

Farage, MA et al. Cognitive, sensory, and emotional changes associated with the menstrual cycle: a review. Arch Gynecol Obstet. 2008 Oct;278(4):299-307.

Baker, F at al. Sleep and 24 hour body temperatures: a comparison in young men, naturally cycling women and women taking hormonal contraceptives. J Physiol. 2001 Feb 1; 530(Pt 3): 565–574.

Charkoudian N et al., Autonomic control of body temperature and blood pressure: influences of female sex hormones. Clin Auton Res. 2017 Jun;27(3):149-155.

Baker, F at al. Circadian rhythms, sleep, and the menstrual cycle. Sleep Med. 2007 Sep;8(6):613-22.

Shilaih M et al. Modern fertility awareness methods: Wrist wearables capture the changes of temperature associated with the menstrual cycle. Biosci Rep. 2017 Nov 24.

Tenan MS, et al. Changes in resting heart rate variability across the menstrual cycle. Psychophysiology. 2014 Oct;51(10):996-1004.

de Zambotti, M el al. Autonomic regulation across phases of the menstrual cycle and sleep stages in women with premenstrual syndrome and healthy controls. Psychoneuroendocrinology. 2013 Nov;38(11):2618-27.

Brar TK, et al. Effect of Different Phases of Menstrual Cycle on Heart Rate Variability (HRV). J Clin Diagn Res. 2015 Oct;9(10):CC01-4.

Baker, F at al. Oral contraceptives alter sleep and raise body temperature in young women. Pflugers Arch. 2001 Aug;442(5):729-37.

Teixeira, AL et al. Heart rate variability across the menstrual cycle in young women taking oral contraceptives. Psychophysiology, 52 (2015), 1451–1455.

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