Ah, the menstrual cycle. So misunderstood by many, but so important for all.

The menstrual cycle starts with the first day of your period and ends the day before your next period, but the amount of time in between varies more than people expect. The 28-day cycle many people are familiar with is actually an average, so by the very nature of averages, some cycles are longer and some are shorter — and that’s totally natural. In fact, the length of the menstrual cycle can vary from person to person AND from cycle to cycle for each individual throughout life (1). The normal range for a cycle is anywhere from 21 to 35 days. So if your average cycle is 35 days long, that’s still considered normal (2). Cycle length could also be affect by a bunch of factors like age, genetics, smoking, diet, exercise, stress levels (2, 3)… so basically all the things.

The menstrual cycle consists of 3 phases: the follicular phase, the ovulatory phase, and the luteal phase (4). We’re going to talk about what happens in your body for each of these phases and what signs or symptoms you might expect during each phase. This can be especially helpful if you’re using fertility awareness methods to chart your menstrual cycle.

The follicular phase

The follicular phase starts on the first day of your period and ends on the day of ovulation. This phase is so named because follicle stimulating hormone (FSH) causes about 15-20 eggs to begin maturing in each ovary, which are enveloped in their own follicle (5), a fluid-filled sac (6). The greatest variation in any given cycle will usually be in this phase because the maturation process could last anywhere from 8 to 21 days. But eggs take about 2 weeks to mature on average (5).

During this phase, your basal body temperature (BBT)*, which is your body’s lowest temperature in a 24-hour period (7), tends to be lower, and you may have sticky, tacky cervical mucus (CM) or even no CM (8).

The increased amount of estrogen released by the follicle causes a few different things to happen in your body. Your cervix and the ligaments holding it in place respond to estrogen, lifting the cervix higher, and softening and opening it to allow sperm to pass through. If you’re charting your cycle and tracking cervical position, you’ll feel the progression and a palpable difference, especially around ovulation. Estrogen is also what makes the egg from the largest follicle to push through the wall of the ovary, which leads us to the next phase (5).

An increase in luteinizing hormone (LH), called the LH surge, will also be triggered up to 36 hours before the egg is released; this is when the ovulation phase begins (9).

*Our bodies don’t usually reach their lowest temperature (BBT) until sometime between 3am and 6am when most of us are asleep (10). So when we chart temperatures for our menstrual cycles, we use waking temperature as an approximation for BBT, but the temperature we record every morning is not true basal body temperature. Many resources don’t make this distinction when talking about BBT and charting your menstrual cycle, but it’s important to understand the difference as more advanced temperature recording devices are created.

The ovulation phase

Ovulation is the release of a mature egg from the ovary. When LH reaches its peak, the egg will be released about 10 to 12 hours later (9). In the days leading up to and on the day of ovulation, you may experience more fertile CM, characterized by higher water content. It may be egg white CM, which is stretchy and looks exactly like ti sounds, or it may be so watery that the only evidence of it is a circular wet patch on your underwear (5, 11).

After the egg is released, the follicle that housed the mature egg collapses, becoming the corpus luteum (meaning “yellow body”), and starts to release progesterone. The other eggs and follicles that had begun developing will disintegrate (5).

The day after ovulation, the increase in progesterone causes your waking temperature to spike, which is referred to as the temperature shift. When this shift from low to high temperatures is sustained for at least 3 days, it suggests that ovulation occurred; however, in some individuals, ovulation my happen without this temperature spike (8).

The luteal phase

The luteal phase starts the day after ovulation (the same day as the temperature shift) and ends on the day before your next period. The corpus luteum has a limited lifespan of about 12 to 16 days, which is why the luteal phase tends to have less variation than the follicular phase (2). The corpus luteum releases many different hormones, but progesterone dominates this phase (12) and is the reason higher waking temperatures are sustained until the start of your period (13).

In response to progesterone, the endometrium, or lining of the uterus, thickens to prepare for implantation and pregnancy (12). The lower levels of estrogen cause your cervix to drop, become firm, and close up (14). Your CM will also start to dry up, and you may not see any more until after your period; though you may experience some fertile-quality CM during the luteal phase (5).

If the egg isn’t fertilize, the uterine lining will shed, your period will begin (15), the corpus luteum will disintegrate (16), and you’ll enter the follicular phase to start the process anew.

If the egg is fertilized and becomes an embryo, that’s a whole different story! Your body will use the lining that was developed since the embryo will implant in the uterus (15), the corpus luteum will live on (16), and the pregnancy will progress in a whole other amazing process.

In closing

So there you have it: The menstrual cycle in a nutshell. With up to 21 days for the follicular phase and 16 days for the luteal phase, that’s quite different from the 28-day cycle we’re all led to believe we “should” have. Definitely check in with your doctor if you’re concerned about your health, but if your cycles aren’t 28 days, that’s ok — you do you (3)!

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References

1. Fehring, R. J., Schneider, M., & Raviele, K. (2006). Variability in the phases of the menstrual cycle. Journal of Obstetric, Gynecologic, & Neonatal Nursing, 35(3), 376-384.
2. Mayo Clinic. (2019, June). Menstrual Cycle; What’s normal, what’s not.
3. Clancy, K. (2010, December). I don’t have a 28-day menstrual cycle, and neither should you. Scientific American.
4. Knudtson, J., McLaughlin, J. (2019, April). Female Internal Genital Organs. Merck Manual Consumer Version.
5. Weschler, T. (2015). Taking Charge of Your Fertility: The definitive Guide to Natural Birth Control, Pregnancy Achievement, and Reproductive Health.
6. National Cancer Institute. (n.d). Ovarian follicle. NCI Dictionary of Cancer Terms.
7. B S, H., K, D., R C, M., T G, K., & A, P. (2022). Novel Technique for Confirmation of the Day of Ovulation and Prediction of Ovulation in Subsequent Cycles Using a Skin-Worn Sensor in a Population With Ovulatory Dysfunction: A Side-by-Side Comparison With Existing Basal Body Temperature Algorithm and Vaginal Core Body Temperature Algorithm. Frontiers in bioengineering and biotechnology, 10, 807139.
8. Mayo Clinic. (2018, November). Basal body temperature for natural family planning.
9. Reed, B. G., & Carr, B. R. (2018). The normal menstrual cycle and the control of ovulation. In Endotext [Internet]. MDText. com, Inc..
10. Kelly, G. (2006). Body temperature variability (Part 1): a review of the history of body temperature and its variability due to site selection, biological rhythms, fitness, and aging. Alternative medicine review, 11(4).
11. Planned Parenthood. What’s the cervical mucus method of FAMs?
12. Mesen, T. B., & Young, S. L. (2015). Progesterone and the luteal phase: a requisite to reproduction. Obstetrics and Gynecology Clinics, 42(1), 135-151.
13. Forman, R. G., Chapman, M. C., &Steptoe, P. C. (1987). The effect of endogenous progesterone on basal body temperature in stimulated ovarian cycles. Human Reproduction, 2(8), 631-634.
14. Our Bodies, Ourselves. (2014, April). Charting Your Menstrual Cycle.
15. Planned Parenthood. (n.d.). Menstruation.
16. Liu HC, Pyrgiotis E, Davis O, Rosenwaks Z. Active corpus luteum function at pre-, peri- and postimplantation is essential for a viable pregnancy. Early Pregnancy : Biology and Medicine : the Official Journal of the Society for the Investigation of Early Pregnancy. 1995 Dec;1(4):281-287. PMID: 9363260.

Feature photo by Anete Lusina

Originally posted on Kindara.com blog