Everything You Didn't Know About Periods

I’ve been receiving so many questions pertaining to amenorrhea (absent periods) and PCOS over on my Instagram that I figured it’s time to lay the groundwork for some future posts about reproductive health, pregnancy, and more! Today, we’re going way back to the basics - but adding in details you probably missed in health class, my favorite resources to learn about reproduction, and even what a thermometer can tell you about your cycle.

Disclaimers: this post is intended for educational purposes only and does not serve as a substitute for medical advice. Please bring all medical concerns to your personal physician or healthcare provider(s). This post contains affiliate links, which means we may make a small commission off of purchases made through these links - any commission we make comes at no additional cost to you. Thank you for supporting the Satisfy blog!

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The Menstrual Cycle - What Really Happens

Now let’s get into details. The menstrual cycle is divided into two (or three, if you count ovulation) phases:

  1. Follicular phase (from day 1 of your period to ovulation)

  2. Ovulation

  3. Luteal phase (from ovulation to the day before day 1 of your next period)

The whole cycle is run by a network of different hormones - here’s a quick acronym to help you remember them:


The Follicular Phase

In the follicular phase, follicle stimulating hormone (FSH) stimulates each ovary to begin to mature about 15-20 eggs. Each egg matures its own follicle (think of this as a fluid-filled sac around the egg), and each follicle produces estrogen. Once estrogen reaches a certain level (called the estrogen threshold - this varies from person to person), luteinizing hormone (LH) is produced. LH is the hormone that causes the actual act of ovulation and stimulates an egg to pass through the ovarian wall.

The Luteal Phase

The egg’s follicle hangs behind in the ovary and earns a new name - the corpus luteum, which stays on the ovarian wall and produces progesterone. Progesterone stops other eggs from being released and causes the endometrium to start thickening (if pregnancy occurs, the fertilized egg needs a nice, fluffy endometrium to attach to and begin to grow). When the corpus luteum dies off (about 12-16 days after ovulation), progesterone drops, the endometrium sheds (your period), and the cycle restarts.

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Cycle Length

The follicular phase typically lasts 14-21 days and the luteal phase about 12-16 days, making for an average cycle length of 28-35 days. A few things to note…

  • The luteal phase length is typically consistent within 1-2 days for each body, so if yours is usually 13 days, it will likely always be 12-14ish days.

  • The follicular phase is more variable in length because it’s more highly affected by stress and other factors.

  • In the first 5-7 years of having a period, cycles vary a lot more. They’re also more variable about 10 years before menopause.

How do I know if and when I ovulate?

Monitoring fertility signs can be helpful in determining whether you’re ovulating and when.

Cervical Fluid

Cervical fluid changes throughout the follicular phase, becoming more and more fertile as you get closer to ovulation (which makes sense, since it’s the medium that sperm swim through to find the egg). If you’re interested in what the pattern looks like (heads up - there’s pictures), you can learn more about the cervical fluid cycle here.

Basal Body Temperature

Basal body temperature (basal meaning when you first wake up) can also be a way to keep tabs on your cycle. BBT follows what’s called a bi-phasic pattern (same as your cycle) and the marker between phases is ovulation (also same as your cycle). In the follicular phase, estrogen suppresses BBT. In the luteal phase, progesterone elevates BBT - so in a zoomed out view, your temp should be low for the first portion of your cycle then higher for the second portion. If you’re looking to learn more about how to track this and determine when a temperature shift has actually happened, I highly recommend the book Taking Charge of Your Fertility (heads up - there’s a small amount of diet and weight talk, but the overall focus is on cycles). Note: you do need a specific basal body thermometer to take these readings - they’re a little more precise and read a lower range of temps than a fever thermometer, which is what’s probably in your medicine cabinet.

Cervical Height

With the exception of around ovulation, the cervix is generally low in the vagina, firm, closed, and not wet. Around ovulation, it becomes SHOW: soft, high, open, and wet. This is more of a supporting sign used alongside monitoring cervical fluid and BBT.

Ovulation Predictor Kits (OPKs)

These are over-the-counter at-home urine tests (they essentially look like a pregnancy test) which measure the surge of luteinizing hormone to predict ovulation within a few days. Most come with a guide to help determine when to test based on your cycle length (so you’re not just using tests at random and spending more money).

Why does it matter if I ovulate or get a period?

Sexual and reproductive function can be affected by several factors, including inadequate energy intake (not eating enough). In bodies with uteruses, a regular period can be a good indicator that overall health is good - it’s a sort of gauge for how things are going in general.

Undernutrition from chronic dieting, overexercising, or an eating disorder can (but not always) cause the loss of a cycle or irregular cycles.

Some other important points…

  • All bodies menstruate at different weights and points in recovery from dieting or eating disorders, so the weight at which you get your period will likely be different from other stories you’ve heard. This also means that providers cannot predict if & when you will regain your period - it’s a leap of faith, but one your body is asking you to make.

  • Continuing to have a period doesn’t mean you’re not “sick enough” to seek help with your relationship with food or an eating disorder. If you want help or if your relationship with food and your body is interfering with living out your values, you deserve help.

A Quick Note

This post may not personally apply to your body if: you’re on hormonal birth control, pregnant, live in a biologically male body, or are walking the process of gender affirmation. However, I do believe that knowledge is power and everybody should have a working understanding of how bodies work, so this post is still for you.

On the Birth Control Pill?

Because the mechanism of hormonal birth control is to prevent ovulation, any bleeding that occurs while on the Pill or another HBC is not a “true” period. In this context, regularity of periods is not a reliable gauge of overall health. That being said, birth control and sexual safety are a highly personal topics that should be made between you and your partner. There are certainly other indicators of health and recovery that can be used, but I hope this information was helpful.

Irregular Periods?

If you’re concerned about the length of time between cycles, painful or heavy periods, absent periods - or, frankly, anything - speak to your doctor about next steps.


  • Gaudiani J. Sick Enough: A Guide to the Medical Complications of Eating Disorders. New York: Routledge; 2019.

  • Welt C. 2017. Physiology of the normal menstrual cycle. UpToDate. Updated March 17, 2017. Accessed January 23, 2019.

  • Weschler, T. Taking Charge of Your Fertility. New York: Harper Collins; 2015.