Why Your Period Feels So Unpredictable in Your 40s, and What LOOP Cycles Have to Do With It
By: Jill Chmielewski, October 30, 2025
If your periods have started to feel unpredictable or all over the place in your 40s, it's not just random. It's actually part of the perimenopause transition. There are real physical reasons for this, based on how your hormones interact with each other. Once you understand these patterns, it all starts to make a lot more sense.
The First Domino to Fall: When the Signals Start to Fade
Menopause doesn’t begin the day your periods stop. It starts years earlier, when the delicate communication between your brain and ovaries begins to change.
Here’s how I often explain it to my clients: When your ovarian reserve is healthy, your brain quietly suggests, “Hey ovaries, time to grow another egg.” The ovaries respond easily, ovulation happens on cue, and estrogen and progesterone rise and fall in rhythm. Your cycle is regular and predictable.
But as the number of available follicles (eggs) naturally declines with age, your brain has to work harder to get a response. It starts to “raise its voice,” sending stronger hormonal signals through FSH (follicle-stimulating hormone). It’s your body’s way of adapting to a changing internal landscape.
Your Body’s Early Messengers: AMH, Inhibin B & the Corpus Luteum
Hormones are messenger molecules, constantly signaling between your brain and your ovaries. And as perimenopause approaches, three of these messengers begin to shift: AMH, Inhibin B, and the Corpus Luteum.
AMH: Your “Egg Reserve Report Card”
Anti-Müllerian Hormone (AMH) is made by the small, resting follicles in your ovaries, the ones quietly waiting for their chance to mature. AMH tells your brain roughly how many follicles remain in reserve. As this pool gradually declines with age, AMH levels drop, often years before your cycle changes. This makes AMH one of the earliest clues that your reproductive system is beginning to downshift.
Inhibin B: The “Feedback Signal”
Inhibin B is made by follicles that are actively growing, the ones responding to your brain’s message to develop an egg. When many follicles are growing, Inhibin B rises and sends a calm, reassuring message back to the brain:
“We’ve got this… You can quiet down the FSH.”
But as the follicle count drops, Inhibin B declines. The brain no longer hears that quiet reassurance, so it “turns up the volume,” increasing FSH. That louder signal recruits multiple follicles at once, which is what leads to the hormonal chaos of early perimenopause: irregular cycles, estrogen surges, and unpredictable ovulation.
The Corpus Luteum: Your Progesterone Factory
After ovulation, the empty follicle transforms into a golden structure called the corpus luteum (Latin for yellow body). Its entire job is to produce progesterone for about two weeks.
Progesterone calms the brain, steadies the mood, balances estrogen levels, supports sleep, and maintains a stable uterine lining. If fertilization doesn’t occur, progesterone drops, the corpus luteum dissolves, and your next period begins. But when ovulation becomes inconsistent, as it often does in perimenopause, no corpus luteum forms. No corpus luteum means no progesterone, and without that soothing, stabilizing hormone, everything feels a little more chaotic.
The Hormone Cascade: From a Whisper to a Shout
As AMH and Inhibin B decline, your brain loses some of its ability to fine-tune FSH. The entire conversation between the brain and the ovaries becomes louder and less coordinated. FSH surges. Eggs mature at irregular times. Estrogen spikes unexpectedly.
Estrogen levels can soar sky high while progesterone remains low, creating an imbalance often referred to as estrogen dominance. It’s not that you suddenly have too much estrogen; it’s that you have too little progesterone to balance and modulate estrogen.
When Ovulation Falls Out of Rhythm
As this back-and-forth between your brain and ovaries becomes less coordinated, ovulation itself can start happening at unusual times, or sometimes not at all. This is where things start to feel unpredictable.
Some months, your body might release an egg early, late, or skip ovulation entirely. At other times, more than one follicle may grow and mature simultaneously, causing estrogen levels to rise in waves rather than in a single, smooth peak.
These irregular patterns are what we call LOOP cycles — luteal-out-of-phase cycles, when the luteal phase (the progesterone-producing part of the cycle) falls out of sync with the follicular phase (the estrogen-producing part).
The result? Hormonal surges that can feel like chaos: mood swings, sleep issues, heavier bleeding, and cycles that come closer together. But what feels like instability is actually your body’s transition in motion, an intricate recalibration as it adapts to fewer available eggs and shifting feedback loops.
The Progesterone Piece: The First to Fall
Progesterone is the first hormone to decline as ovulation becomes inconsistent. If you don't ovulate, you don't make a corpus luteum. Without that, your body can't make much progesterone.
Low luteal-phase progesterone means:
FSH isn’t suppressed → cycles shorten
Estrogen levels continue to rise, causing the uterine lining to become thicker.
Periods become heavier or prolonged.
This is when you might notice those heavy or 'flooding' periods that can feel overwhelming. Providing your body with real progesterone at this stage can be highly beneficial. It doesn't force your cycle into a set pattern. It helps your body regain hormonal balance.
The Problem With Silencing Your Hormones
Many women are given birth control pills (BCPs) to 'regulate' cycles during these perimenopausal hormone swings. But BCPs replace natural hormones with synthetic chemicals and suppress communication between the brain and ovaries. Things might seem calmer for a while, but you lose your body's natural rhythm in the process, and those hormone signals are what keep everything working well (throughout the body, beyond just reproduction).
What the Pill Actually Does
Most birth control pills combine two synthetic hormones:
Ethinyl estradiol is a synthetic estrogen. It's much stronger than your body's own estradiol and can raise your risk of blood clots and inflammation.
Progestins (synthetic progesterone) do not calm the brain, protect breast tissue, build bones, or balance estrogen signals in the breast.
The result is that many women spend years, sometimes even a decade or more, on synthetic chemicals (under the auspice of hormones) that shut down the very messengers that keep their brains sharp, their bones strong, and their mood steady.
So what does your body lose when hormones are suppressed? Let's explore two key hormones and their roles:
Progesterone - Your body’s mood stabilizer
Supports deep sleep
Calms anxiety and steadies mood
Balances estrogen’s effects on breast and uterine tissue
Supports thyroid, blood sugar regulation, and immune system function
Synthetic progestins don't give you these benefits. In fact, they can make you feel more irritable and inflamed.
Testosterone — The Drive, Strength, and Vitality Hormone
Builds muscle and bone
Boosts energy, libido, and motivation
Supports cognitive clarity and confidence
The pill raises SHBG, a protein that attaches to your testosterone and lowers the amount that's free in your body. That's the hormone that gives you strength and energy.
There are times when BCPs may be appropriate, but women deserve complete transparency and to be informed of all associated risks and benefits. Many women take BCPs for years without understanding their effects or risks, like blood clots, mood changes, bone loss, or nutrient loss. I know doctors who have treated young women in their 20s and 30s who developed blood clots while on the pill. Many of them were never warned that such an outcome could occur, and the impact was catastrophic.
So, this is not about bashing BCPs. It’s about informed education and helping women understand what BCPs actually do, so they can make decisions that feel aligned with their goals and values.
What’s ironic is that many of the same clinicians who defend long-term BCP use are quick to label HRT (Hormone Restoration Therapy) as “dangerous,” when in truth, our bodies know and thrive with our own optimized, bioidentical hormones. It’s dangerous to demonize our body’s natural hormones while promoting synthetic chemicals that come with a slew of risks and side effects.
A Note on the “Pill Debate”
Lately, I’ve noticed more conventional medical providers expressing frustration that birth control pills (BCPs) seem to be “getting a bad reputation.” I understand that irritation. This isn’t about the pill suddenly becoming villainized or “falling out of favor.” It’s about the fact that BCPs have been used for decades as a universal solution to almost every menstrual or perimenopausal concern. often without a true, informed consent conversation.
Many women were reassured that the pill would "regulate" their cycles, but the reality is that the pill overrides your natural rhythm by replacing your body's hormonal communication with synthetic signals.
Even the newer oral contraceptive, Nextstellis, is being marketed as a gentler, more modern pill which contains two hormones: Estetrol (E4) and Drospirenone.
It sounds innovative, but before anyone calls it a game-changer, let’s look more closely at what it actually is, and isn’t.
Let’s break down what’s in these newer options, starting with Estetrol (E4).
Estetrol (E4) is one of four known human estrogens (alongside estradiol, estrone, and estriol). Estetrol is only produced naturally by babies in utero, specifically by the fetal liver, and it circulates in both the fetus and the mother during pregnancy. Its purpose in the body isn’t fully understood, and outside of pregnancy, we neither produce nor utilize estetrol. Although it’s being praised as a “weaker,” more selective estrogen, its long-term safety data are limited.
Some people claim that estetrol is superior because it is “plant-based” and more environmentally friendly (because it breaks down more easily in the body and waterways compared to older synthetic estrogens like ethinyl estradiol, the one responsible for much of the ecological damage associated with hormonal contraceptives). Remember, “plant-based” does not mean “bioidentical.” Bioidentical refers to a hormone’s molecular structure, not its source. Whether a compound is grown on a shrub or synthesized in a lab doesn’t matter; what matters is whether it’s identical to the hormones your body naturally makes.
Now let’s consider the other key hormone in Nextstellis: drospirenone.
The progestin in Nextstellis, drospirenone, isn’t new. It’s the same synthetic progestin found in many popular BCPs. Pharmacologically, drospirenone has anti-mineralocorticoid effects (meaning it can counteract bloating or water retention) and anti-androgenic effects (which may reduce acne). But those same actions can also block testosterone activity, and testosterone is essential for women’s energy, motivation, mood, and libido. While some may notice clearer skin or reduced bloating, others may experience a lower mood, reduced drive, or fatigue. It’s also worth noting that drospirenone has been linked to a slightly higher risk of blood clots compared to some other progestins.
So, in light of all this, what practical steps can you take as your hormone signals change?
Support your physiology instead of suppressing it.
At its peak, your body makes up to 100 times more progesterone than estrogen. When estrogen goes up and down a lot in perimenopause, your body needs more progesterone to restore balance. This often means more than the usual 100 to 200 mg progesterone capsule offered in standard care.
Many of my colleagues use a combination of oral, transdermal, and vaginal progesterone in much higher doses than 100-200 mg to ensure progesterone-to-estrogen balance. Choose the progesterone method that works best for you to support hormone balance and ease perimenopausal symptoms. Prioritize informed choices that align with your goals and physiology as your hormone levels change. Progesterone pioneers like Dr. Jerilynn Prior and Dr. Katharina Dalton have demonstrated that physiologic levels of progesterone, rather than synthetic progestins, support mood, sleep, bone health, and emotional steadiness.
Final Thoughts
Early perimenopause isn't about low estrogen. It's about erratic estrogen fluctuations and not having enough progesterone. When you understand LOOP cycles, you have words for what's going on and the knowledge to make good choices about your care, birth control, and hormone therapy.
If you want to understand how to use progesterone to support your body naturally, watch our previously recorded progesterone webinars with progesterone experts Phyllis Bronson, PhD, and Carol Petersen, RPh, where we walk through forms, doses, and what your symptoms might be telling you. I’ve also included links to learn more about Birth Control Pills.
Disclaimer: This article is for educational and informational purposes only and is not intended to replace personalized medical advice or individualized care. It is meant to help you understand your physiology, explore evidence-based options, and make informed choices about your health and wellness. Healthcare should be a partnership, not a permission slip, and proactive care is just as essential as treatment. Use this information to engage in open, collaborative discussions with your provider or to make empowered decisions that align with your own values, goals, and comfort level. You are the ultimate authority on your body.