What is happening to my periods?
Irregular, heavier, lighter, skipped, unpredictable — changing periods are the #1 first sign of perimenopause, affecting around 90% of women. Yet almost no one explains what is actually happening or why. Rose does.
Rose
"The first thing that changed for me was my cycle. It became unpredictable in a way it never had been — earlier some months, later others, heavier than I thought possible. My doctor ran tests, told me everything was normal, and sent me home. Nobody said the word perimenopause. I had to find that word myself."
Key takeaways
✓Changing periods are the #1 first sign of perimenopause — affecting around 90% of women in their 40s
✓The change can go in any direction — shorter cycles, longer gaps, heavier bleeding, lighter flow, or completely unpredictable patterns
✓Heavy flooding is driven by estrogen dominance when ovulation (and therefore progesterone) becomes irregular
✓Skipped periods in perimenopause do not mean you cannot get pregnant — contraception is still needed until 12 months after the final period
✓Heavy perimenopausal bleeding causes significant iron loss — ferritin should be checked, not assumed
✓Progesterone supplementation is often the most targeted treatment — it directly counteracts the cause of flooding
✓Always rule out other causes of abnormal bleeding — fibroids, polyps, and endometrial changes need to be excluded
Why periods change in perimenopause
The menstrual cycle is controlled by a precise hormonal conversation between the brain, the ovaries, and the uterus. In perimenopause, that conversation becomes erratic — and the period is where the disruption shows up most visibly.
As the ovarian reserve declines, ovulation becomes inconsistent. Some months it happens normally. Some months it happens late. Some months it does not happen at all. Each of these variations produces a completely different hormonal pattern — and therefore a completely different bleeding experience.
The key hormonal shift is the drop in progesterone that comes with anovulatory cycles (cycles where no egg is released). Progesterone is only produced after ovulation — so no ovulation means no progesterone. Without progesterone to regulate the uterine lining, estrogen acts unopposed — building the lining thicker and longer than usual before it finally sheds, often heavily and with clots.
The six ways periods change — and why each one happens
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Cycles getting shorter
Periods arriving every 21-24 days instead of 28. The first phase of the cycle (follicular) shortens as fewer follicles are available. This often begins in the early 40s and is one of the earliest signs of perimenopause.
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Cycles getting longer or skipping
Gaps of 35, 45, 60 days or more between periods. Ovulation becomes erratic — sometimes it happens, sometimes it does not. Each skipped ovulation is a month without progesterone, which has downstream effects on mood, sleep, and bleeding.
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Heavier bleeding
Flooding, clots, soaking through protection in an hour. Without the counterbalancing effect of regular progesterone, estrogen can build up the uterine lining unchecked between periods — producing heavier, sometimes alarming, bleeds when it finally sheds.
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Lighter or shorter periods
Periods that last 1-2 days instead of 4-5, or are noticeably lighter. As ovarian function declines, estrogen levels drop — less uterine lining builds, less sheds. This is common in later perimenopause.
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Unpredictable spotting
Light bleeding between periods, mid-cycle spotting, or staining that does not follow any pattern. Erratic estrogen fluctuation can trigger breakthrough bleeding as the lining responds to hormonal shifts rather than a predictable cycle.
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Worse PMS than ever before
Symptoms that used to be manageable become severe — cramping, mood changes, breast tenderness, bloating. The hormonal swings of perimenopause amplify PMS in many women. What was tolerable at 30 can become disabling at 44.
When to see a doctor — do not wait for these
See your doctor if you experience any of these
⚠Bleeding that soaks through a pad or tampon in an hour or less for several consecutive hours
⚠Bleeding that lasts longer than 7 days
⚠Bleeding between periods (spotting) that is new and recurring
⚠Any bleeding after 12 months without a period — this is postmenopausal bleeding and always needs investigating
⚠Severe pelvic pain accompanying the bleeding
⚠Symptoms of anaemia — extreme fatigue, breathlessness, dizziness, heart racing
Abnormal bleeding always needs an examination to exclude fibroids, polyps, endometrial hyperplasia, and other causes before assuming it is perimenopause alone.
The contraception question — yes, you still need it
Perimenopause does not mean infertility
Erratic periods do not mean ovulation has stopped — it means it is unpredictable. Any cycle where ovulation does occur carries the possibility of pregnancy. Women in perimenopause continue to conceive — sometimes unexpectedly.
Contraception is recommended until 12 months after the final period (for women over 50) or 24 months after (for women under 50). If you are using the pill or hormonal IUS for cycle management, this also provides contraception. If you are using non-hormonal HRT, you still need contraception separately.
What actually helps — evidence graded
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Progesterone supplementation
Strong evidence
Oral micronised progesterone (body-identical) is the most evidence-backed intervention for heavy perimenopausal bleeding. It counteracts the estrogen dominance that drives flooding and clotting. This is also HRT — and it is often prescribed specifically for cycle regulation before estrogen is added.
Evidence-backed benefits
• Directly counteracts estrogen-driven endometrial build-up
• Reduces flooding and clot-passing in the majority of women
• Improves sleep as a side effect — progesterone is naturally calming
• Body-identical micronised form (Utrogestan) has a better side-effect profile than synthetic progestins
How to use this
This requires a prescription. Ask specifically for micronised progesterone — not medroxyprogesterone acetate (synthetic progestin). It can be used cyclically (days 14-28) or continuously depending on your pattern.
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Hormonal contraception
Strong evidence
The hormonal IUS (Mirena), combined pill, or mini-pill can regulate or stop periods entirely. These are used by many doctors as a first-line response to perimenopausal bleeding — they work, but they mask the hormonal picture rather than addressing it.
Evidence-backed benefits
• Mirena IUS is highly effective at reducing or stopping bleeding within 3-6 months
• Combined pill regulates cycles and reduces bleeding significantly
• Can provide contraception simultaneously — important as pregnancy is still possible in perimenopause
How to use this
Worth discussing if bleeding is severely disrupting your life. Note that the pill will suppress your natural hormone fluctuations — this means it may mask other perimenopausal symptoms and make them harder to track.
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Tranexamic acid
Moderate evidence
A non-hormonal medication that reduces the volume of bleeding by helping blood clot more efficiently in the uterus. Used only during heavy bleeding days — it does not affect hormones or cycle timing.
Evidence-backed benefits
• Reduces bleeding volume by up to 50% in clinical studies
• Non-hormonal — suitable for women who cannot or prefer not to use hormones
• Taken only on heavy days — no daily commitment
How to use this
Prescription required. Taken at the first sign of heavy flow and continued for the duration of heavy days. Discuss with your doctor if flooding is significantly affecting your life.
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Anti-inflammatory diet
Moderate evidence
Reducing refined carbohydrates, sugar, alcohol, and ultra-processed foods reduces systemic inflammation that worsens bleeding. Increasing omega-3-rich foods (oily fish, flaxseed) has prostaglandin-modulating effects that may reduce cramping and flow.
Evidence-backed benefits
• Reduces prostaglandins that drive cramping and heavy flow
• Lowers insulin — which affects estrogen metabolism
• Alcohol specifically worsens heavy bleeding and should be avoided in the days before a period
How to use this
Avoid alcohol in the 3-5 days before your period is due. Increase oily fish, walnuts, and flaxseed. Cut refined carbohydrates and sugar particularly in the second half of your cycle.
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Magnesium
Moderate evidence
Magnesium deficiency worsens cramping, PMS, and heavy bleeding. Magnesium relaxes uterine muscle and has prostaglandin-modulating effects. Most perimenopausal women are deficient.
Evidence-backed benefits
• Reduces uterine cramping by relaxing smooth muscle
• Modulates prostaglandins that drive heavy flow
• Improves perimenopausal mood and sleep as secondary benefits
How to use this
300-400mg magnesium glycinate daily, taken in the evening. Effects on period symptoms build over 2-3 cycles.
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Iron supplementation
Strong evidence
Heavy perimenopausal bleeding causes iron loss — often significant. Iron deficiency is extremely common in women with flooding and causes fatigue, hair loss, brain fog, and breathlessness. This needs to be tested and treated, not just assumed.
Evidence-backed benefits
• Replaces iron lost through heavy bleeding
• Ferritin above 70 ng/mL is the target — not just being out of the anaemia range
• Correcting iron deficiency significantly improves energy, hair, and cognitive function
How to use this
Ask for ferritin (not just haemoglobin or serum iron). Ferritin under 30 needs supplementation. Bisglycinate form has fewer digestive side effects than standard ferrous sulphate. Take with vitamin C, away from calcium and thyroid medication.
What to say to your doctor
The conversation that gets you taken seriously
"I am in my [age] and my periods have become [describe: heavier/irregular/flooding/unpredictable]. I would like to discuss whether this is perimenopause, and if so, whether progesterone supplementation or other hormonal management is appropriate. I would also like my ferritin checked — I understand heavy bleeding causes significant iron loss that is often missed."
Full doctor conversation guides — with scripts for six key appointments →
Rose on this
"The most frightening bleed I ever had was in perimenopause — a flooding episode that sent me to A&E. Nobody had told me this was possible. Nobody had explained that without regular ovulation, my lining could build up unchecked and shed dramatically. Understanding the mechanism did not stop it happening — but it stopped me thinking I was dying. That is worth something."
From Rose
"Changing periods are not a disorder. They are the body signalling a transition — loudly, sometimes alarmingly, but not randomly. Understanding why it is happening is the first step to managing it. And there are real options. You do not have to just endure this."
What we do not know yet
?Why some women experience flooding while others experience lighter periods in perimenopause — individual variation in endometrial sensitivity to estrogen fluctuation is not well characterised
?The optimal progesterone dose and timing for cycle regulation in perimenopause — current protocols are largely extrapolated from contraceptive and HRT research rather than perimenopause-specific trials
?Whether dietary and lifestyle interventions meaningfully reduce heavy perimenopausal bleeding in their own right, or only as adjuncts to hormonal management
Written by
Rose
Navigating perimenopause · Researcher · Founded rosemyfriend.com
Research basis
PubMed · Cochrane reviews · NICE guidelines · British Menopause Society · The Menopause Society
Read methodology →
Rose provides evidence-graded educational information — not medical advice. Always discuss health decisions with a qualified healthcare provider.
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