Missing Periods (Amenorrhea): What Your Cycle Is Telling You

A menstrual cycle is not just about fertility. It is a monthly readout of how several systems — brain, thyroid, ovaries, adrenal glands, uterus — are talking to each other. When periods stop, one of those conversations has broken down. The useful question is never "how do I get my period back," but "what is the reason it left."

What a normal cycle actually looks like

There is a wider normal range than most people are told.

• Cycle length: 24 to 38 days, counted from the first day of one period to the first day of the next.
• Bleeding days: up to 8 days.
• Variation: in adults, cycle-to-cycle variation of up to 7 to 9 days is still considered regular.
• Volume: enough that you change a pad or tampon every few hours on your heaviest day, not every 30 to 60 minutes.

Teenagers get a grace period. In the first year or two after the first period, cycles are often irregular while the brain-ovary feedback loop matures. By roughly three years after menarche, most cycles settle into the adult range.

Changes worth an appointment: periods that stop for three months or more, cycles consistently shorter than 21 days or longer than 45 days in an adult, bleeding between periods, bleeding after sex, bleeding after menopause, or a sudden change in your own established pattern. "My periods used to be like clockwork and now they aren't" is a legitimate reason to be seen, even if everything sounds normal on paper.

Primary versus secondary amenorrhea

Primary amenorrhea means periods never started. We evaluate when there has been no period by age 15 with normal breast development, or by age 13 with no signs of puberty at all. Don't wait longer than that — some of the causes are structural or chromosomal, and they are easier to address earlier.

Secondary amenorrhea means periods started and then stopped — conventionally three months of no bleeding in someone with previously regular cycles, or six months in someone whose cycles were already irregular.

The distinction matters because it narrows the list before we run a single test.

Causes, roughly in the order we think about them

Pregnancy — always tested first

This is not a formality. Pregnancy is the single most common cause of a missed period, including in women using contraception, women who believe they cannot conceive, and women in perimenopause. Every workup for a missed period starts with a pregnancy test. It costs almost nothing and it changes everything downstream.

Hypothalamic amenorrhea

The hypothalamus stops sending the pulses that drive the ovary. This is usually a response to low energy availability — not eating enough for the amount of energy you are burning — and it does not require being underweight. Common settings: heavy training, distance running, dance, restrictive eating patterns including "clean eating," rapid weight loss, and prolonged psychological stress or illness.

Athletes may hear this described as part of RED-S (relative energy deficiency in sport), which extends beyond periods to bone, immune function, mood, and performance. The loss of periods is often the first visible sign, and it is not a benign adaptation to training.

Polycystic ovary syndrome

PCOS is the most common cause of chronic irregular or absent ovulation. It typically shows up as infrequent periods plus signs of excess androgen — acne along the jaw, coarse hair growth on the face, chest, or abdomen, hair thinning at the scalp — and often, but not always, insulin resistance. It is a diagnosis of exclusion: we rule out the mimics before we label it.

Thyroid disease

Both an underactive and an overactive thyroid disturb cycles. Hypothyroidism in particular can cause absent periods, heavy periods, or elevated prolactin. It is cheap to test and straightforward to treat, which is why TSH is on the first round of labs.

Hyperprolactinemia

Elevated prolactin suppresses ovulation. Causes include a benign pituitary adenoma (prolactinoma), medications — especially antipsychotics, some antidepressants, metoclopramide — hypothyroidism, and chest wall stimulation. Milky nipple discharge, headaches, or changes in peripheral vision raise the suspicion and warrant pituitary imaging.

Primary ovarian insufficiency

When the ovaries stop functioning before age 40, we call it primary ovarian insufficiency. It affects roughly 1 in 100 women. It often comes with hot flashes, night sweats, vaginal dryness, and poor sleep, and it is confirmed with repeated elevated FSH levels alongside low estradiol. POI is not the same as early menopause — intermittent ovarian function and even pregnancy remain possible — but it does require hormone therapy until the typical age of menopause, for bone and cardiovascular protection.

Asherman's syndrome and structural causes

Scar tissue inside the uterus, usually after a D&C, uterine infection, or surgery, can prevent the lining from building and shedding. The clue is amenorrhea that started right after a uterine procedure, sometimes with cyclic pelvic pain and no bleeding. In primary amenorrhea, structural causes include an imperforate hymen, a transverse vaginal septum, or Müllerian agenesis, where the uterus never fully developed.

Other contributors: significant systemic illness, poorly controlled diabetes or celiac disease, and hormonal contraception — some methods, particularly the hormonal IUD and progestin-only options, thin the lining so that periods become light or absent. That is an expected effect, not a problem to be fixed.

What the workup looks like

It is usually a short list, not an odyssey.

1. Pregnancy test, without exception.
2. A focused history: age at first period, the pattern before it stopped, weight and training changes, stress, medications, headaches or vision change, nipple discharge, hot flashes, prior uterine procedures, and family history of early menopause.
3. An exam, including assessment of androgen signs and, in primary amenorrhea, external and internal anatomy.
4. First-line labs: TSH, prolactin, FSH, estradiol. Add testosterone and other androgens if PCOS is suspected.
5. Pelvic ultrasound when anatomy is in question or PCOS is on the table.
6. Selected additional testing: pituitary MRI for elevated prolactin, karyotype in primary amenorrhea or POI under 30, hysteroscopy or saline ultrasound if intrauterine scarring is suspected.

Bring a record of your cycles if you have one. A tracking app screenshot is genuinely useful data.

Why missing periods matter for your bones

This is the part that gets underplayed. Estrogen protects bone. Peak bone mass is largely built by the late twenties, and prolonged low estrogen during those years means you never reach the peak you should have — and then you start the normal age-related decline from a lower starting point.

Women with hypothalamic amenorrhea have measurably lower bone density and higher rates of stress fractures. In young athletes this is a real, current injury risk, not a distant one. The longer amenorrhea lasts, the more bone is at stake, and some of it does not come back. Amenorrhea lasting six months or more, or a history of stress fractures, is a reason to consider a DXA bone density scan.

Importantly, putting someone on a combined oral contraceptive to "restore" a period does not fix this. It produces a withdrawal bleed and masks the underlying signal without correcting the energy deficit or reliably protecting bone. Treating the cause does.

Treatment follows the cause

• Hypothalamic: increase energy intake, reduce training load, address disordered eating with a dietitian and, where relevant, a therapist. Periods usually return, though it can take several months. Adequate calcium and vitamin D throughout.
• PCOS: manage the specific problem in front of us — cycle regulation and endometrial protection with hormonal contraception or cyclic progestin, androgen symptoms, metabolic risk, or ovulation induction if pregnancy is the goal. See menstrual issues and infertility care.
• Thyroid disease: correct the thyroid, and cycles typically follow.
• Hyperprolactinemia: dopamine agonist medication, or treat the underlying cause such as a contributing drug or hypothyroidism.
• Primary ovarian insufficiency: hormone therapy until the average age of menopause, plus bone monitoring and a conversation about fertility options. See hormone therapy and menopause management.
• Asherman's: hysteroscopic removal of adhesions, usually with measures to prevent them reforming. See gynecological surgery.
• Structural causes in primary amenorrhea: surgical correction where appropriate, with counseling matched to the specific anatomy.

One more note on endometrial protection: if you have PCOS or chronic anovulation and go many months without bleeding, the uterine lining can build up under unopposed estrogen. Over years, that raises the risk of endometrial hyperplasia and cancer. This is why we do not simply ignore infrequent periods, even when pregnancy is not a concern.

A missing period is information. Most causes are treatable, several are simple, and the ones that are not still benefit enormously from being found early. If your cycle has changed, book an appointment rather than waiting to see whether it sorts itself out.

Medical disclaimer

This article is for general education and does not replace individual medical advice. Menstrual changes have many possible causes, and the right evaluation depends on your age, history, and examination. Please discuss your own symptoms with Dr. Adeeb Alshahrour or another qualified clinician before making decisions about testing or treatment. If you have heavy bleeding with dizziness or fainting, severe pelvic pain, or a positive pregnancy test with pain or bleeding, seek care the same day.