How do hormones change during this period?

Summary

In perimenopause, hormones do not decline in an orderly way. They fluctuate for years, sometimes peaking higher than they did in your reproductive years, and only then settle at a permanently low level. That fluctuation is why symptoms come and go, and why one month feels fine and the next does not. It is also why a single blood test tells you only part of what your body is doing that day. This is why Lumia does not show you "your hormone level today", but the typical pattern — with its variability made explicit — alongside the data you record yourself.

What is happening?

In your reproductive years the cycle is regulated by a feedback loop between the brain (the hypothalamus and pituitary) and the ovaries: FSH released by the pituitary matures a follicle, the follicle produces estrogen, and after ovulation the remaining tissue secretes progesterone. As the egg reserve falls, that loop loosens and the hormones begin to change at different speeds ¹:

• AMH (anti-Müllerian hormone): Reflects the number of follicles left, and is the first to fall — it starts declining years before menopause. It shows the reserve, but it does not explain symptoms.

• Progesterone: One of the early decliners. In cycles where ovulation is skipped or weak, not enough progesterone is produced. This is an important reason why the gaps between periods change, why bleeding gets heavier, and why sleep and mood are disturbed.

• FSH: The brain raises FSH to compensate for the ovaries' fading response. But in perimenopause FSH does not rise in one direction. Over months it moves back and forth between high and normal values.

• Estrogen (estradiol): The most misunderstood hormone here. In perimenopause it is produced irregularly and sometimes excessively rather than simply declining. Follicles stimulated by the rising FSH create high estrogen peaks from time to time. The permanent fall happens as the final period approaches, and after it.

• Testosterone: Does not drop suddenly at menopause; it declines slowly with age from your twenties onwards. The ovaries carry on producing some after menopause too.

After the final period the picture simplifies: estradiol is permanently low, FSH is permanently high, and the main source of estrogen is no longer the ovary but estrone, a weaker form of estrogen produced in fat tissue.

What do we know?

• Fluctuation is the rule, not the exception: The SWAN cohort, which followed the menopausal transition for years, showed that estradiol and FSH vary widely from woman to woman and, in the same woman, from month to month — and that the permanent change accelerates about two years before the final period ². The endocrinology of perimenopause is not "a tap closing slowly" but "a tap shuddering" ³.

• A single measurement doesn't tell you the stage: NICE states that measuring FSH is not necessary in women over 45 with typical symptoms, because the result can differ even within the same month. Measurement is meaningful in specific situations, such as suspected premature ovarian insufficiency under 40 ⁴.

• AMH roughly predicts the timing of menopause, not the symptoms: In the SWAN data, very low AMH indicates that the final period is approaching. But that prediction works on the scale of years, and it bears no relation to the severity of hot flashes ⁵.

• Hot flashes are triggered by estrogen "withdrawal" — both its fall and its fluctuation: The neurons that regulate temperature in the hypothalamus (KNDy neurons) become overactive when estrogen is withdrawn, and they narrow the body's "comfort range" for temperature. This is why symptoms begin in late perimenopause, when estrogen is at its most erratic, are at their most intense in early postmenopause, and can continue for years after estrogen has settled at a permanently low level ⁷. Some of the newer non-hormonal medicines target exactly this mechanism (see the separate article on non-hormonal options).

• Testosterone deficiency is not diagnosed from a blood level: International consensus states that testosterone levels in women show no reliable relationship with sexual desire or energy, and that measurement should be used only to rule out an excessively high level ⁶.

What does this give you?

• Symptoms coming and going is ordinary: A bad week after two good ones does not mean the treatment "isn't working" or that you are "getting worse". Most of the time what you are feeling is the fluctuation itself. Your tracking data makes that pattern visible.

• Periods of high estrogen cause symptoms too: Complaints such as breast tenderness, bloating and heavy bleeding run counter to the expectation that "estrogen is falling" in perimenopause — but they are precisely part of this fluctuation. Headache attacks also become more frequent in this period: what triggers migraine is a sudden drop in estrogen, and fluctuation makes those drops more frequent.

• Why progesterone falling early matters: Because of its effects on sleep, anxiety and the menstrual pattern, doctors sometimes look at the progesterone side first in perimenopause. That is a treatment decision, and it is made only with your doctor.

• Don't read a blood result on its own: The conclusion "my FSH came back normal, so I'm not in perimenopause" can be wrong. Your doctor interprets the result together with your age, your menstrual pattern and your symptoms.

The hormone graphic in Lumia shows the typical pattern by stage, and the band of variability within that pattern. It is not your personal hormone level. Your own cycle and symptom records can be placed beside that graphic, and comparing the two gives you something concrete to take to your doctor.

Sources

1. Harlow SD, et al. Executive summary of the Stages of Reproductive Aging Workshop + 10. Menopause. 2012;19(4):387-395.
2. Randolph JF, et al. Change in follicle-stimulating hormone and estradiol across the menopausal transition. J Clin Endocrinol Metab. 2011;96(3):746-754.
3. Prior JC. Perimenopause: the complex endocrinology of the menopausal transition. Endocr Rev. 1998;19(4):397-428.
4. NICE. Menopause: identification and management (NG23). 2015; updated November 2024.
5. Finkelstein JS, et al. Antimullerian hormone and impending menopause in late reproductive age. J Clin Endocrinol Metab. 2020;105(4):e1862-e1871.
6. Davis SR, et al. Global Consensus Position Statement on the Use of Testosterone Therapy for Women. J Clin Endocrinol Metab. 2019;104(10):4660-4666.
7. Rance NE, et al. Modulation of body temperature and LH secretion by hypothalamic KNDy neurons. Front Neuroendocrinol. 2013;34(3):211-227.

Related articles

• Perimenopause, menopause, postmenopause: what do the stages mean? 5 min read
• FSH and estradiol: what blood tests do and don't tell you 5 min read
• Hot flashes and night sweats 5 min read
• Progesterone and the cycle: why does it fall first in perimenopause? 5 min read