Heavy periods during the perimenopause

Heavy periods during the menopause - Hormone Health
Why does menstrual bleeding become heavier and irregular during the perimenopause?

In this article Dr Patrick Bose, Hormone Health Associate and Consultant Gynaecologist, examines the menstrual cycle in greater detail and explains the reasons behind why periods become heavier and irregular during perimenopause and why it is important to discuss this with your doctor.

For many women, one of the early signs of the perimenopause is increasingly heavier and irregular periods. Normal cycles last between 21-35 days with duration of bleeding lasting from 2-7 days. A regular ‘28 day’ cycle is actually quite rare and cycle lengths vary considerably particularly around puberty and the perimenopause.

Control of the menstrual cycle

Control of the cycle begins deep inside the hypothalamus of the brain, where Gonadotrophin releasing hormone (GnRH) activates the pituitary gland to secrete follicle stimulating hormone (FSH) and lutenising hormone (LH).

Females are born with 2 million eggs, most degrade by puberty (300,000) and by the menopause the number of healthy eggs has fallen to less than 10,000. Maturing eggs are protected within fluid filled cysts called ovarian follicles and are maintained in a state of suspended animation until reactivated prior to ovulation.

Each month, rising levels of FSH stimulate these follicles, reawakening the eggs from their arrested state to complete development. Several follicles are stimulated at any one time, but only one egg becomes the dominant follicle, destined for release at ovulation.

Because these maturing follicles take on a ‘cyst’ like appearance they can be readily visualised with ultrasound (fluid is black on USS). The levels of FSH and LH levels required to stimulate and mature a single healthy egg are normally low but when the quality and number of the egg falls, the signal required to cause ovulation needs to be much higher.

This is why FSH/LH levels rise significantly during the perimenopause.


We routinely measure FSH and LH with a Pan 2 hormone test. This test gives us lots of valuable information about your cycle and remaining fertility. A persistent rise in FSH infers there are few viable follicles remaining, and menopause is approaching.

Ultrasound can visualise the actual number of follicles in the ovary (follicle count) to further assess fertility. If there are too many follicles/cysts, the ovary might be described as ‘polycystic’ possibly suggesting endocrine imbalances such as Polycystic Ovary Syndrome PCOS.

In other instances we prevent release of GnRH using medications such as zoladex/synarel etc to temporarily interrupt the natural cycle, and thus manage severe life threatening hormone imbalances such as Premenstrual Dysphoric Disorder PMDD.

Understanding the Ovulation Cycle

Around the middle of the cycle, a surge of lutenising hormone signals the ovary to squeeze out its most dominant follicle (ovulation), sending the unfertilised egg towards the uterus via the fallopian tubes.

Some women notice this as mid-cycle pain. Fertilisation by sperm must take place within 12-24 hours, or the egg will no longer be viable. The embryo will attach to the wall of the uterus around five days after ovulation, thus establishing a pregnancy.

The cystic area that remains where the follicle initially developed becomes known as the corpus luteum. Luteninsing hormone signals the corpus luteum to produce another important hormone, progesterone.


Levels of progesterone levels peak around day seven days before the next expected bleed, (hence the name day 21 progesterone test in a 28 day cycle). Levels > 30nmol/l are a sign of successful ovulation. Although the cyclical nature of progesterone is essential for regulation of the cycle, progesterone is also responsible for the debilitating emotional and behavioural symptoms of PMS/PMT.

Classic symptoms include, anxiety, mood swings, irritability, anger, abdominal bloating, fluid retention, skin changes , insomnia and poor concentration span. In some cases sensitivity to progesterone is so severe that it dangerously impacts on mental health – Premenstrual Dysphoria Disorder (PMDD).

Conversely, progesterone supplements can be used to control irregular bleeding; support early pregnancy after IVF; and also to reduce pregnancy loss after late miscarriage.

Balancing the Hormonal Symphony

Whilst LH stimulates progesterone, FSH stimulates oestrogen production. Oestrogens primarily originate from the ovaries but also in small amounts from the adrenal glands and fat cells.

In the early part of the cycle, oestrogens act in combination with progesterone to cause proliferation of the endometrium (womb lining) in readiness for implantation of a fertilised egg, a process called decidualisation. Decidualisation is a complex process that thickens the endometrium with blood vessels and stromal cells, ‘organising’ it into a lush environment ready for the embryo to implant and develop. A careful balance of oestrogen and progesterone is essential to maintain a regular, smooth and healthy endometrium.

What are the warning signs of endometrial cancer?

Any disruption in the balance of oestrogen and progesterone leads to abnormal thickening. If left unchecked, endometrial thickening may cause irregular uterine bleeding. Persistent irregular bleeding in perimenopausal women may thus be a warning sign of possible endometrial cancer.


Risk factors associated with development of endometrial cancer are abnormal bleeding, obesity, not having had children, polycystic ovary syndrome, early menarche and late menopause. Post menopausal bleeding should therefore prompt urgent investigation by your GP.


Endometrial thickness less than 5mm is key to excluding possible endometrial cancer. Ultrasound is not only effective at identifying abnormal configuration, but can also exclude benign pathologies that cause heavy painful irregular bleeding such as uterine polyps, fibroids and adenomyosis etc.

This is why if you experience irregular bleeding, particularly around the menopause or whilst taking HRT, you will be offered an urgent scan. If the endometrial thickness is persistently raised, you might require an endometrial biopsy and/or investigation by one of our associated gynaecologists. When identified early, endometrial cancer is relatively easy to treat.

The Menstrual Phase of the Cycle

Without a fertilised egg to nurture there is no need for the body to retain the decidualised endometrium. Also, without the corresponding corpus luteum to produce progesterone, levels falls abruptly causing the decidualised endometrium to detach from the underlying uterine muscle.

Approximately 80ml of blood and tissue is expelled each month, usually around 14 days after ovulation. The underlying endometrium then undergoes ‘decidualisation’ again, prior to the next cycle of stimulation and ovulation etc. Uterine contraction and passage of clots through the cervix, cause painful abdominal cramping. This process of menstruation lasts 2-7 days.

Stages of Menstrual Cycle

So fundamentally, a regular cycle or ‘period’ requires the sequential coordination of seven events:

  1. Hypothalamic release of pituitary hormones FSH and LH
  2. Stimulation of a viable follicle (egg) by FSH/LH
  3. Ovulation of a single dominant follicle
  4. Contraception to avoid Fertilisation
  5. Progesterone withdrawal from failing corpus luteum
  6. Decidualisation of endometrium to properly ‘organise’ tissue
  7. Menstruation to expel redundant organised tissue.

We simulate this natural cycle by correcting imbalances of oestrogen and progesterone using the combined oral contraceptive pills in woman with irregular cycles. Lower doses of these same oestrogens and progesterones are contained in in HRT.

Artificial body identical oestrogens (eg oestradiol gel/patches/creams/sprays and micro-ionised progestogens (utrogestan capsules/mirena IUS) are common examples of the treatments we commonly prescribe to alleviate symptoms and improve quality of life in perimenopause.

This article was written by Hormone Health Associate Dr Patrick Bose BSc PhD FRCOG

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