Women Are Not Little Men with Uteruses: The Four Phases of the Female Cycle

Women, you are not little men with a uterus. This should be painfully obvious. Except it isn’t at all, because it is not remotely how we have approached women’s health for the last several decades.

The entire medical and wellness infrastructure of this country was built around male physiology. Men run on a roughly 24-hour hormonal cycle. Testosterone peaks in the morning, runs down through the day, resets overnight. And that is the rhythm that most research got built on, which means it’s the cycle most fitness advice and nutrition guidance assumes.

To be clear, it’s not because researchers are biased against women. The reason much of the foundational research was done primarily on men is that they were trying to protect women, particularly women of reproductive age, from experiments or tests that could harm their ability to get pregnant, stay pregnant, or protect the child growing inside of them.

But the unintended consequences have been devastating.

A healthy cycle runs roughly 21 to 35 days, and that cycle governs virtually everything: a woman’s mood, energy, cognition, libido, immune function, stress response, and yes, even who you’re attracted to.

So in this article we’re diving into:

• How hormones influence far more than just reproduction
• The fifth vital sign
• The four phases of the female cycle
• The best charting methods (with “success” rates)
• FemTech: real, or just well-funded?
• Additional curricula, books, and websites

Hormones Shape Who You Are

Dr. Sarah Hill is a psychologist at Texas Christian University and the author of a genuinely groundbreaking book called This Is Your Brain on Birth Control. One of my favorite insights from her book is that we tend to think of hormones as just existing and affecting women “down there,” but the reality is that hormones exist and help govern a woman’s entire body, from her mind on down. Moreover, the hormonal fluctuations women experience across their cycle are not incidental to who they are. They’re deeply tied to how women think, feel, learn, connect, and choose partners. Which means when you suppress that system or ignore it, you’re not just preventing pregnancy. You are diminishing and rejecting an entire dynamic system that, in part, makes you who you are.

Now, I am not saying that we are mere animals who should be governed by our hormones or impulses. Nor am I saying we should rely on an artificial pill to shut them down. Instead, especially as Christians, we should learn how our bodies work, so that we can govern our bodies with knowledge and wisdom. That’s a big part of what it looks like to love and honor the glorious and good bodies that God gave us. So, let’s dive in.

The Fifth Vital Sign

In 2015, the American College of Obstetricians and Gynecologists (ACOG) said that a woman’s menstrual cycle should be listed as the fifth vital sign because it is central to understanding the health and well-being of a woman. Sadly, outside of restorative reproductive medicine practitioners, almost no doctor asks a woman to chart her cycle or teaches her how to do it.

And, even if a woman does, most standard OGBYN’s don’t know how to utilize it. It isn’t a required part of medical training, so it isn’t a required part of an appointment. This is a massive oversight and loss because a well-kept chart can surface things before bloodwork or imaging catch them: whether you’re ovulating at all, whether your progesterone is doing its job, whether your thyroid might be off, and early signals of PMOS or endometriosis.

The Four Phases of the Female Cycle

A normal, healthy cycle runs anywhere from 21 to 35 days. And only about 5 to 10 percent of women have what we’d call a textbook 28-day cycle. And yet that number —28 — is baked into period apps, medical intake forms, and our cultural understanding of the female cycle that the vast majority of women are benchmarking their bodies against a cycle length that doesn’t actually apply to them. This matters, especially, when it comes to tracking your cycle, identifying your ovulation window, and diagnosing infertility and reproductive health conditions.

Within the cycle window, there are four phases: menstruation, the follicular phase, ovulation, and the luteal phase.

Phase one: menstruation

Your cycle begins on day one — the first day of full flow (not just when/if you “spot”). Getting “day one” right is essential for tracking the rest of one’s cycle.

So what’s going on inside the body? Estrogen and progesterone, two of the central hormones in a woman’s body, are at their lowest point during menstruation. The uterine lining sheds, because no pregnancy occurred last cycle. And at the same time, a hormone called FSH, or follicle-stimulating hormone, starts rising to recruit a whole new group of follicles for the cycle ahead. This phase typically runs two to seven days.

If you’re a woman, I don’t need to tell you how it feels: fatigue, cramping, low energy, and the desire to lie in bed with a heating pad, dark chocolate, and a good movie. And while you may not always feel great, it’s also important not to view your body as the enemy or your cycle as an attack against you. While you may feel bad, your body is doing something orderly, purposeful, and extraordinary: it is shedding, clearing, and rebuilding your reproductive potential for the month ahead.

At the same time, painful periods may be common, but common doesn’t mean normal. Merlot Fogarty wrote for Natural Womanhood about teenage years marked by extreme pelvic pain, heavy bleeding, and mood swings, and how she just assumed that she was simply weak, dramatic, or unlucky. Nobody had told her that her body might be trying to say something was wrong. It wasn’t until a Creighton intro session in her junior year of college that she heard, for the first time, that such pain isn’t normal.

In Merlot’s case, it was undiagnosed stage IV endometriosis. If she had just gone on birth control to manage the symptoms, she never would have had the opportunity to treat her condition, and her own ability to have children would have been seriously threatened.

So let me say this as clearly as I can: If your cycle is wildly inconsistent, or lasts a single day, or is so heavy that you’re bleeding through a pad or tampon every hour for multiple hours in a row — that is not normal. Severe pain is not something you’re supposed to just live with. It points to something that isn’t functioning the way it ought to.

And rather than reaching first for a birth control pill that will suppress the symptoms, we should be asking what’s actually going on.

Phase two: the follicular phase

The follicular phase begins on day one of your cycle (yes, it overlaps with menstruation) and runs all the way until ovulation.

This is the most variable phase of the cycle, and it’s the reason cycle lengths differ so much between women, and from month to month within the same woman.

As FSH rises, it stimulates multiple follicles in the ovaries to start developing, and the “dominant” one produces the egg that a woman releases at ovulation. As it grows, it produces estrogen, and estrogen does two things. It thickens the uterine lining to prepare to “catch” and implant a possible human embryo (if sperm fertilizes the egg that month). And it triggers the production of fertile-quality cervical mucus, which is what selects and helps sperm survive and travel. (Cervical mucus is a natural “sifter” killing unhealthy or abnormal sperm.)

During this phase, you’ll feel your energy rising, mood lifting, and more sociable. This is when a woman’s libido (sexual “desire) starts climbing. Research also shows that verbal fluency and social cognition actually peak in the late follicular phase for women, such that this is when women tend to feel their sharpest, most outward-facing selves.

This is also the phase that is most vulnerable to disruption due to stress, illness, travel, big changes in sleep, or dramatic swings in exercise or body weight. Any of these things can delay ovulation by stretching out the follicular phase.

Phase three: ovulation

Ovulation is the event the entire first half of your cycle has been building toward. It’s the main attraction. And it’s also one of the briefest phases of the cycle.

A surge of luteinizing hormone (LH) from the pituitary gland triggers the dominant follicle to rupture, and a mature egg is released into the fallopian tube. The egg itself survives only 12 to 24 hours. That is all the time sperm has to fertilize the egg. Still, a woman’s fertile window is six to seven days total: the five days before ovulation, plus the day of ovulation itself. Why? Because sperm can survive up to five days inside a woman’s body.

Which means if you’re trying to conceive, the best days are the two to three days immediately before ovulation, so the sperm are already in position. If you wait until you see a positive LH strip to have sex, the window is already closing.

This is where regular “period apps” are so off base: Ovulation occurs about 14 days before your next period begins. Not 14 days after your last period ended.

So for example, if your cycle is 35 days long, you’re likely ovulating around day 21, not day 14. If your cycle is 25 days, you may be ovulating around day 11. That day-14 assumption is hardcoded into almost every period app on the market, and for the majority of women, it’s simply inaccurate.

So how do you know ovulation is coming? Your cervical mucus transitions from a thick, white, milky substance into something clear and stretchy, roughly the consistency of raw egg white. A positive ovulation predictor kit or LH strip will confirm the hormone is rising. And a lot of women notice increased libido right around then, too.

And how do you know it’s already passed? The cervical mucus dries up quickly, and your basal body temperature rises and stays elevated.

In short: Mucus predicts. Temperature confirms. Cervical mucus changes before ovulation, so it tells you the window is opening. Basal body temperature rises after, so it can only tell you ovulation already happened.

Phase four: the luteal phase

After ovulation, the empty follicle transforms into something called the corpus luteum. Which sounds like a spell you’d hear about from Harry Potter but is actually a remarkable feat where the woman’s body takes the spent follicle and repurposes it into a temporary hormone-producing gland.

And what it produces is progesterone. Progesterone does several things at once. It prepares the uterine lining for implantation next month by thickening it. It causes your basal body temperature to stay elevated. And it thickens cervical mucus into a barrier at the cervix. Of all four phases, the luteal phase is the most stable. In most women it lasts 12 to 16 days and stays fairly consistent from cycle to cycle.

The Best Charting Methods

• Sympto-Thermal — Basal body temperature plus cervical mucus, with cervical position optional. Sensiplan, the best-studied version, reports 99.6% perfect use and 98.2% typical use when learned from an instructor. Works well with irregular cycles because it reads real-time signs rather than calendar history. Start with Taking Charge of Your Fertility by Toni Weschler. This is basically the approach we use.

• Creighton Model — Cervical mucus only, using a standardized recording system reviewed by a trained FertilityCare Practitioner. Perfect use: 99.5%. It’s also the foundation of NaProTechnology, which uses cycle charts to diagnose and treat PMOS, endometriosis, recurrent miscarriage, infertility, and thyroid disorders at the root rather than suppressing symptoms.

• Billings Ovulation Method — Cervical mucus judged by sensation rather than appearance alone. Perfect use: approximately 99%. No thermometer, no device, nothing to buy, which is why it has been taught successfully worldwide to women of every literacy level, and why it’s the only method usable by the visually impaired.

• Marquette Model — Uses the Clearblue Fertility Monitor to track estrogen and LH in urine daily (Low / High / Peak), with mucus and temperature optional. Typical use: 95–98%. Built specifically for the hard cases, including irregular cycles, PMOS, postpartum, breastfeeding, perimenopause. This is the one to look at when mucus or temperature alone are difficult to read, or when you’re in a season where tracking is just harder.

• FEMM — Cervical mucus with optional LH strips and detailed symptom logging, with the strongest health-monitoring orientation of the group. FEMM trains providers to read charts clinically, so this is my recommendation for women working through hormonal problems, especially when conceiving isn’t the immediate goal.

• Calendar apps and the rhythm method — Typical use: 76–80% at best, with roughly 21% of predictions accurate in any given cycle. This is not a fertility awareness method. It uses no real-time information from your body. If you see a single wide effectiveness range quoted for “fertility awareness,” it’s usually because calendar methods have been averaged in with the instructor-taught methods above.

  One note that matters more than the method you pick: the single biggest predictor of success is whether you learned from a trained, certified instructor. That variable accounts for essentially the entire gap between perfect use and typical use across every method on this list. Instruction generally runs $100–$500 and may be covered by insurance or an HSA.

FemTech: Real, or just well-funded?

I have no financial or official relationship with any of these. I’ve either used them, tried them, or the research on them is solid. There are hundreds of fertility tracking products for sale. One app is currently FDA-cleared for birth control.

• Natural Cycles — The first and only FDA-cleared birth control app in the US, cleared as a Class II medical device in 2018, and cleared separately for use with the Oura Ring. Uses basal body temperature from an oral thermometer, the Oura Ring, the NC Band, or a compatible Apple Watch, and marks each day green or red. 93% typical use, 98% perfect use — comparable to condoms. Those figures are for the app alone, not paired with mucus observation or any of the methods above.
• Mira — A different category entirely. Measures actual hormone levels in urine — LH, estrogen, a progesterone metabolite, FSH — as real numbers rather than positive/negative. Dip a wand, insert it into the analyzer, get values in about 21 minutes. Its model is trained on more than 950,000 cycles. Not FDA-cleared for contraception, which Mira states plainly, but nothing on the consumer market shows you your hormonal pattern in more detail. Named Fast Company’s most innovative fertility company in 2024. ~$199 for the device, then $45–80/month for wands. HSA/FSA eligible.
• Kegg — An intravaginal device that measures electrolyte changes in cervical mucus to estimate the fertile window. Two minutes daily, synced to an app. A conception tool only, it’s not a contraceptive. It also works as a Kegel exerciser, which is a strange but real bonus. $249 one time, no subscription. HSA/FSA eligible.
• Oura Ring — Not an FDA-cleared contraceptive on its own. A wellness wearable that estimates ovulation and cycle phase alongside sleep, HRV, and heart rate. Paired with Natural Cycles it carries that clearance; without the integration it’s a useful awareness tool, not a method. A 2025 peer-reviewed JMIR study validated its temperature-based ovulation detection across 1,155 cycles and found it roughly three times more accurate than calendar-based tracking.
• Skip these — Flo: 77 million monthly users, calendar-algorithm predictions, and an FTC investigation over sharing user health data with third parties including Facebook and Google, settled in 2023. If the privacy of your health data matters to you, this isn’t the one. And any generic calendar app that only asks for period dates and predicts from averages is a digital rhythm method delivering roughly 21% accurate predictions.

Curricula, Books, and Websites

• Natural Womanhood — naturalwomanhood.org. Founded 2012 by Anna and Gerard Migeon; nonprofit focused on body literacy and restorative reproductive medicine. They have the FAM Basics series, the Cycle Symptom Checklist, and the Period Genius program for mothers/daughters.
• Elevate / The Body Literacy Project — thebodyliteracyproject.org and katievidmar.com. Katie Vidmar created Elevate (a training program for healthcare professionals) and founded The Body Literacy Project, which works with leaders in policy and education. Elevate is a 1.5-hour staff in-service using a script and flip chart for teaching body literacy in-clinic.
• FACTS About Fertility — factsaboutfertility.org. Run by Dr. Marguerite Duane, this website is chock-full of research, resources, and provider information.
• Books: Taking Charge of Your Fertility (Weschler) · This Is Your Brain on Birth Control (Hill) · The Fifth Vital Sign (Hendrickson-Jack) · The Language of Your Body (Valenzuela)