Perimenopause: fluctuating hormones and irregular cycles
Perimenopause is the transition into the menopause, when the ovaries respond erratically, oestrogen and progesterone swing up and down, and periods become irregular.
Remember
In perimenopause the hormones swing up and down unpredictably, rather than switching off, so symptoms often begin while periods are still happening.
Perimenopause is the transition into the menopause (the menopause itself is confirmed only after 12 months without a period). During it the ovaries do not simply switch off. Instead they respond erratically to FSH and LH (follicle-stimulating hormone and luteinising hormone, the signals that normally drive egg development and ovulation), so ovulation becomes unpredictable and the output of oestrogen and progesterone swings up and down.
As the supply of follicles (the small egg-containing structures in the ovary) steadily runs down, ovulation becomes less frequent and less predictable. Fewer ovulations mean less progesterone is made, while oestrogen swings up and down and can at times rise above normal. Some cycles are anovulatory (no egg is released). With no ovulation there is no corpus luteum (a temporary structure that makes progesterone), so oestrogen acts on the lining of the womb without its usual opposing partner. This is unopposed oestrogen: the lining keeps growing unevenly and then sheds unpredictably, so periods can become irregular, light or heavy.
The same instability disturbs the feedback between the ovaries, the hypothalamus and the pituitary gland. These hormonal swings are linked to vasomotor symptoms (hot flushes and night sweats, thought to involve the temperature-control centre in the hypothalamus), mood changes and sleep disturbance, which can appear while periods are still occurring. FSH and LH tend to rise overall because the ovaries respond less well, but FSH itself fluctuates.
Ovulation can still happen, so contraception is still needed if pregnancy is not wanted. Persistently low oestrogen is the picture after the menopause, not in the perimenopause.
Key facts
- Hormone pattern
- hormone levels swing up and down in the perimenopause, and oestrogen falls significantly only later.
- Irregular bleeding
- it is typically due to anovulatory cycles: no ovulation means no progesterone, so oestrogen stimulates the lining of the womb unopposed and it sheds erratically.
- FSH and LH
- they tend to rise overall as the ovaries respond less well, but FSH itself fluctuates.
- FSH testing
- because FSH swings during the transition, a single FSH blood test is an unreliable marker.
- Timing
- hot flushes and night sweats usually begin before periods stop.
- Fertility
- ovulation can still occur, so contraception is still needed if pregnancy is not wanted.
- Menopause
- it is confirmed only after 12 months without a period.
Exam traps
- Symptoms in the perimenopause do not come from an abrupt and complete loss of ovarian oestrogen at the final period, because the ovaries keep releasing oestrogen in unpredictable swings for years, and symptoms usually begin before the final period.
- A stable low oestrogen level is the picture after the menopause, not in the perimenopause, where the levels fluctuate and that instability is what makes the stage so symptomatic.
- Falling pituitary FSH and LH release does not explain irregular cycles, because the ovaries respond less and the pituitary gland compensates by releasing more, so levels tend to rise overall but vary in the transition.
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