I don’t order an estradiol level to confirm what a woman already knows about her body. I order it to find out whether the number matches what her bones, brain, and muscle need to keep working well.
I measure estradiol in myself once per quarter. I do the same for patients under my care. I’ve been checking it since my 30s, when I was tracking day 3 estradiol and follicle stimulating hormone (FSH). I do it now to make sure the estrogen I am taking is enough for my bones, brain, mitochondria, cardiometabolic health, and muscle.
Estradiol is the main estrogen circulating in a premenopausal woman’s body, and it varies across the menstrual cycle in a consistent manner. Then it fluctuates wildly in perimenopause and drops in menopause, unless you are on bioidentical hormone therapy.
In the premenopausal woman, the ovaries make most of the estradiol (from the follicle maturing that month), and the amount shifts daily across the menstrual cycle. One of the best times to measure it is day 3, when levels should be 20 to 60 pg/mL (some gynecologists use an upper limit of 50 pg/mL).
Inside the ovarian follicle, two control hormones are involved: luteinizing hormone (LH) tells one type of cell to make androgens (including testosterone), and follicle stimulating hormone (FSH) tells another cell to convert these androgens into estradiol, effectively a two-cell system that produces estradiol.
FSH is the pituitary’s signal to the ovary to do this work. Its job in premenopause is to recruit and grow a follicle each cycle and push that follicle’s cells to make the aromatase enzyme that produces estradiol. In menopause, FSH may be involved in keeping the brain healthier, which is why I check it once a quarter too. Let me know if you want a future post on FSH, the groundbreaking work of Lisa Mosconi, PhD, at Cornell, and why I check it in all of my patients.
Estradiol is central to the menstrual cycle but it has about 300 other jobs too, like maintaining bone, supporting muscle synthesis, shaping blood vessel tone and metabolism, and driving tissue changes in the reproductive tract and breast most women only associate with fertility.
For most of the menstrual cycle, rising estradiol tells the pituitary gland in the brain to ease off. At mid cycle, a high enough level of estradiol flips that signal and triggers the LH surge that causes ovulation. After menopause, when the ovaries stop producing estradiol, estrone (a weaker estrogen made in fat tissue) becomes the main circulating estrogen, unless you are on hormone therapy with estradiol and/or estriol.
In a normal menstrual cycle, estradiol is not one number. It moves from a low point during the first few days of a period to a sharp peak around day 12, before ovulation, usually several fold higher that where it started, before settling into a second rise in the luteal phase. The day the blood is drawn in perimenopause and menopause is part of the result.
In perimenopause, estradiol doesn’t decline in a straight line. It surges, drops, and surges again, sometimes within the same week, before it settles into its postmenopausal range. One blood draw during any of these window tells you little about the underlying pattern. A woman can feel terrible with a number that reads normal, and feel fine with a number that reads low. The fluctuation is part of the diagnosis, and the number in isolation is not.
Once a woman starts estrogen or estrogen/progesterone therapy, the question changes. The number stops being about what whether her ovaries are still functioning and starts being about whether her dose is doing its job. A level checked six weeks into a new estradiol dose tells me about her new steady state, and that’s different than her level before we start hormone therapy.
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What I was taught to order in medical training: *check a day 3 estradiol in a woman with infertility, or a woman with amenorrhea (defined as the absence of menses for >3 months in a woman with previously regular cycles, or >6 months in a woman with previously irregular cycles). We also check estradiol in women undergoing fertility treatment such as in vitro fertilization. Overall, this represents a small minority of women.
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What I do now: *I order a serum estradiol on day 3 in women who are cycling to check estradiol feedback and FSH levels. I measure anti-Mullerian hormone (AMH) to assess ovarian reserve. I track estradiol in perimenopause along with FSH and AMH to assess her timeline to menopause. And I track estradiol in women on hormone therapy to make sure it’s sufficient for our longevity goals. I also track estrogen metabolites in the urine with DUTCH or Genova testing.
Ask for the number itself. If you are already on estrogen therapy, ask what number your current dose produced. Be sure to test the same day after applying the patch so you can compare apples to apples. I perform my quarterly estradiol on day 2 of my patch, about 24 hours after placement.
Note that I’ve been on a stable dose of estradiol patch of 0.1 mg/day for years, and now check my level about once every 6 months.
**What’s your estradiol number? **
**Did anyone interpret it for you? **
Tell me in the comments. I read all of them.
xo, Dr. Sara
Every Friday, I am showcasing one number. One lab test or measurement that matters, explained briefly in a few paragraphs. Cortisol last week, estradiol this week. If the one number earns a place on your reading list, kindly forward it to a woman who is having trouble decoding her labs. Leave a comment below and tell me which number you want next. I will feature whichever you ask for most.
References
Cauley JA, Steroids, 2015.
Geraci A, Frontiers in Endocrinology, 2021.
Mosconi L, et al., Scientific Reports, 2024.
Practice Committee of the American Society for Reproductive Medicine, Fertility and Sterility, 2020.
Rettberg JR, et al., Frontiers in Neuroendocrinology, 2014.
Santoro N, Polotsky AJ, NEJM, 2025.
