Missed Periods: What Could Be Causing It and What to Do Next

What "Missed Period" Actually Means Clinically

Clinicians use two terms. Primary amenorrhea means a period has never arrived by age 15 in someone who otherwise has signs of puberty. Secondary amenorrhea means periods were regular or semi-regular and then stopped for three consecutive months or more, or for six months in someone whose cycles were already irregular. If you have skipped one period, that is not secondary amenorrhea yet, but it is worth investigating. A home pregnancy test answers the most common question in under five minutes.

Oligomenorrhea, the term for cycles that arrive fewer than eight times per year or more than 35 days apart, sits between regular periods and full amenorrhea. Many of the causes overlap completely.

Why Your Menstrual Cycle Is a Vital Sign

The American College of Obstetricians and Gynecologists classifies the menstrual cycle as a vital sign for adolescents and women. That framing matters because a missing period is not just a reproductive inconvenience. It is a signal that the hypothalamic-pituitary-ovarian (HPO) axis, the thyroid, the adrenal glands, or the uterus itself may need attention. Chronic anovulation, regardless of cause, carries downstream risks for bone density, cardiovascular health, and endometrial protection.

The Most Common Causes by Life Stage

The cause of a missed period shifts substantially depending on where you are in your reproductive life. A 19-year-old athlete missing periods has a very different clinical picture from a 47-year-old noticing her cycles becoming sporadic.

Reproductive Years (roughly ages 15 to 45)

Pregnancy is the first thing to rule out. A sensitive urine hCG test can detect pregnancy as early as 10 days after conception. If your test is negative and you are still missing periods, the investigation continues.

Polycystic ovary syndrome (PCOS) affects 8 to 13 percent of reproductive-age women worldwide and is the single most common hormonal cause of irregular or absent periods outside of pregnancy. The Rotterdam diagnostic criteria require two of three features: irregular or absent ovulation, clinical or biochemical signs of excess androgens (think acne, excess hair growth, or elevated testosterone on labs), and polycystic ovarian morphology on ultrasound. Not every woman with PCOS looks the same. You can have PCOS with a normal body weight. You can have it with no visible cysts on ultrasound if your hormone picture fits. ACOG Practice Bulletin 194 covers the diagnostic approach in detail.

Hypothalamic amenorrhea (HA) is the diagnosis when the brain simply stops sending the hormonal signal needed to trigger a period. It accounts for 20 to 35 percent of secondary amenorrhea cases in reproductive-age women. Common triggers include low caloric intake relative to energy expenditure, rapid weight loss, intensive exercise (particularly in endurance sports, gymnastics, or dance), and psychological stress. The Female Athlete Triad, now more broadly called Relative Energy Deficiency in Sport (RED-S), sits in this category. FSH and LH levels are characteristically low-normal, estradiol is low, and there is no withdrawal bleed after a progestin challenge in classic cases.

Thyroid disorders are disproportionately common in women. Hypothyroidism raises prolactin levels and disrupts GnRH pulsatility, producing irregular or absent cycles. Hyperthyroidism can suppress the HPO axis through a different mechanism. A TSH is part of the standard amenorrhea workup. Postpartum thyroiditis deserves specific mention: it affects 5 to 10 percent of postpartum women and can cause a transient hyperthyroid phase followed by hypothyroidism, both of which may delay return of normal cycles after delivery.

Hyperprolactinemia from any cause, whether a pituitary microadenoma, antipsychotic medication, or hypothyroidism, suppresses GnRH and can stop periods entirely. A serum prolactin level is ordered routinely when periods disappear without obvious cause.

Premature ovarian insufficiency (POI) affects roughly 1 in 100 women under age 40. It is not the same as early menopause, because ovarian function can fluctuate and spontaneous pregnancy remains possible. FSH levels above 25 IU/L on two tests taken four weeks apart in a woman under 40 support the diagnosis. POI carries significant implications for bone health and cardiovascular risk, and hormone therapy is recommended until at least age 51.

Trying to Conceive

If you are actively trying to get pregnant, a missed period is the first sign to watch for. A positive pregnancy test is good news, but a missed period with a negative test warrants investigation for anovulation. ASRM guidelines recommend that women under 35 try for 12 months before a formal infertility evaluation, but if periods are already irregular, evaluation should start sooner because anovulatory cycles mean conception is unlikely without intervention.

Postpartum and Lactation

After delivery, the return of periods depends heavily on whether you are breastfeeding. Exclusive breastfeeding suppresses ovulation through elevated prolactin. However, this lactational amenorrhea method (LAM) only meets contraceptive criteria during the first six months and only when breastfeeding is frequent and fully exclusive. WHO guidance on LAM notes a pregnancy risk of less than 2 percent if all three criteria (exclusive breastfeeding, amenorrhea, less than six months postpartum) are met. After six months, or when any supplementation begins, you should not rely on breastfeeding alone for contraception.

Among women who are not breastfeeding, periods typically return within six to eight weeks of delivery. A period that has not resumed by 12 weeks post-delivery warrants evaluation.

Perimenopause (roughly ages 45 to 55, average onset mid-to-late 40s)

Cycle irregularity is the hallmark of perimenopause. Periods may come more frequently, less frequently, be heavier or lighter, or simply skip for months at a time. The STRAW+10 staging system defines early perimenopause as cycle length varying by seven or more days from your usual pattern, and late perimenopause as intervals of 60 days or more between cycles. FSH levels during perimenopause fluctuate too much to be reliably diagnostic on a single test; one elevated FSH does not confirm menopause.

Pregnancy remains possible in perimenopause. Missing a period does not mean you have entered menopause. A pregnancy test is still appropriate before assuming hormonal causes.

Postmenopause

Menopause is confirmed after 12 consecutive months without a period. Any bleeding after that point is called postmenopausal bleeding and requires evaluation to exclude endometrial pathology, not just a shrug about hormones. This is outside the scope of secondary amenorrhea workup, but worth naming because the two questions can be confused.

Less Common but Important Causes

Uterine Causes

Asherman syndrome, the formation of intrauterine adhesions (scar tissue), can block shedding of the uterine lining even when ovulation is happening normally. It most often follows uterine surgery, dilation and curettage (D&C), or severe endometritis. An endometrial biopsy or hysteroscopy can confirm it. Women with this condition may notice they ovulate on ovulation predictor kits but still have no period.

Adrenal Causes

Non-classic congenital adrenal hyperplasia (NCAH) can mimic PCOS and presents with androgen excess and cycle irregularity. A morning 17-hydroxyprogesterone level is the screening test.

Genetic Causes

Turner syndrome (45,X) is the most common chromosomal cause of primary amenorrhea and affects ovarian reserve profoundly. It is usually diagnosed in adolescence but occasionally in early adulthood when the phenotype is subtle.

Medications and Lifestyle Factors That Stop Periods

Several common medications and exposures can suppress or delay periods without representing an underlying disease:

• Hormonal contraceptives: Hormonal IUDs (Mirena, Kyleena), the implant (Nexplanon), the injectable (Depo-Provera), and continuous combined oral contraceptive pills all commonly produce amenorrhea. ACOG guidance notes that with Depo-Provera, up to 50 percent of users have no period after one year of use. This is expected, not dangerous.

• Antipsychotics and dopamine antagonists: Risperidone, haloperidol, and metoclopramide raise prolactin and can suppress periods.

• Chemotherapy and radiation: Gonadotoxic treatment can cause temporary or permanent ovarian failure depending on agent, dose, and age.

• Significant weight changes: Both rapid loss and significant gain can disrupt cycle regularity through different mechanisms.

• Extreme stress: Psychological or physiological stress activates the hypothalamic-pituitary-adrenal (HPA) axis in ways that suppress GnRH. A single catastrophic stressor can delay one cycle; chronic stress can suppress periods for months.

How a Missed Period Is Diagnosed

The workup is not one-size-fits-all. Your clinician will tailor it to your history, but a standard first-line panel for secondary amenorrhea in a reproductive-age woman typically includes the following:

First-Line Blood Tests

| Test | What it rules in or out | |------|------------------------| | Urine or serum hCG | Pregnancy | | TSH | Thyroid disease | | Prolactin | Hyperprolactinemia, pituitary adenoma | | FSH and LH | Premature ovarian insufficiency, hypothalamic suppression | | Estradiol | Ovarian function and estrogen status | | Total and free testosterone | PCOS, adrenal androgen excess | | DHEA-S | Adrenal androgen excess | | 17-hydroxyprogesterone (morning, follicular phase) | Non-classic CAH | | AMH (anti-Mullerian hormone) | Ovarian reserve, adjunct for POI and PCOS |

Imaging

A pelvic ultrasound evaluates the uterus and ovaries, including ovarian morphology for PCOS. If prolactin is elevated or there are symptoms suggesting a pituitary mass (headaches, visual changes), an MRI of the pituitary is ordered.

Progestin Challenge

Administering oral micronized progesterone (typically 200 mg daily for 10 days) and seeing whether bleeding occurs within two weeks helps distinguish between outflow tract obstruction or low estrogen states and anovulation with adequate estrogen. A bleed (a positive challenge) suggests the uterine lining is present and was not being shed due to anovulation. No bleed suggests either low estrogen, an outflow tract problem, or uterine scarring.

Bone Density

If amenorrhea has lasted six months or more, especially with evidence of low estrogen (as in hypothalamic amenorrhea or POI), a DEXA scan is warranted. The Endocrine Society guideline on functional hypothalamic amenorrhea notes that bone loss can begin within months of estrogen deprivation.

Sex-Specific Physiology: Why the Cycle Stops

The HPO axis runs on a precise rhythm. The hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses, which drives the pituitary to release FSH and LH, which in turn drive the ovary to grow a follicle, release an egg, and produce estradiol and progesterone. Anything that disrupts pulse frequency or amplitude anywhere along this axis, whether it is energy deficit, cortisol excess, thyroid hormone imbalance, prolactin excess, or direct ovarian failure, interrupts the sequence. Without the LH surge, there is no ovulation. Without ovulation, there is no progesterone peak. Without progesterone withdrawal, the uterine lining has no trigger to shed.

This framework explains why so many different conditions produce the same symptom. A woman with anorexia and a woman with a prolactinoma may both present with absent periods and low estradiol, but through entirely different mechanisms requiring entirely different treatments.

Women carry an additional layer of complexity: the feedback loops in female physiology involve positive estrogen feedback at mid-cycle (the estrogen surge that triggers the LH surge), a mechanism that does not exist in male physiology. That positive feedback is what makes the female HPO axis uniquely sensitive to disruption. When researchers note that women in clinical trials for GnRH analogues experienced amenorrhea at lower doses than male subjects, this is the biological reason.

When to Worry: Red Flags That Need Prompt Evaluation

Most missed periods have benign or treatable causes. These findings, however, warrant timely evaluation:

• No period at age 15 or no period within three years of breast development
• Sudden loss of periods after they were regular, with no obvious trigger, in a woman under 40
• FSH above 25 IU/L with symptoms of estrogen deficiency (hot flashes, night sweats, vaginal dryness) under age 40
• Galactorrhea (milky nipple discharge) in someone not pregnant or breastfeeding
• Severe headaches or visual field changes alongside amenorrhea (possible pituitary mass)
• Any bleeding after 12 months of confirmed menopause
• Signs of androgen excess (sudden, severe acne; rapid hair growth; voice changes) pointing to a tumor rather than PCOS

Treatment Depends Entirely on the Cause

There is no single treatment for missed periods. What helps one cause may worsen another.

PCOS

Combined oral contraceptives remain first-line for cycle regulation when pregnancy is not desired. Metformin is used where insulin resistance is the main driver. Letrozole is the evidence-based first-line ovulation induction agent per ACOG for women with PCOS trying to conceive, with a live birth rate approximately 27 percent per cycle in the PPCOS II trial.

Hypothalamic Amenorrhea

The only evidence-based primary treatment is nutritional rehabilitation and reduction of exercise load. A 2017 Endocrine Society Clinical Practice Guideline explicitly recommends against prescribing estrogen-progestin contraceptives as a substitute for addressing the underlying energy deficit, because they mask symptoms while bone loss continues. Short-term bone protection may require transdermal estradiol with cyclic progesterone while the underlying cause is being treated.

Premature Ovarian Insufficiency

Hormone therapy with systemic estrogen and progesterone is recommended until at least age 51 for women with POI, primarily for bone and cardiovascular protection. The ESHRE guideline on POI (2016) strongly supports HRT in this population, noting that the risk-benefit ratio differs fundamentally from that in postmenopausal women initiating HRT after 60.

Hyperprolactinemia

Dopamine agonists, cabergoline or bromocriptine, normalize prolactin levels and usually restore periods within weeks to months. A pituitary MRI should precede treatment to characterize any adenoma.

Thyroid Disease

Treating the underlying thyroid disorder (levothyroxine for hypothyroidism, antithyroid medication or radioiodine for hyperthyroidism) typically restores cycles within one to three months of achieving euthyroid status.

Perimenopause

Cycle irregularity in perimenopause does not require treatment unless bothersome. Low-dose combined oral contraceptives can regulate cycles and address vasomotor symptoms in non-smoking, healthy perimenopausal women. The Menopause Society (formerly NAMS) 2022 Hormone Therapy Position Statement supports this approach through menopause transition.

Pregnancy, Lactation, and Contraception

Amenorrhea does not mean you cannot get pregnant. This deserves emphasis because it is frequently misunderstood across all the conditions above.

In PCOS: Ovulation can occur unpredictably even when cycles are widely spaced. Women with PCOS who do not want to conceive need reliable contraception.

In perimenopause: Ovulation continues to occur irregularly until confirmed menopause (12 full months without a period). ACOG Committee Opinion 734 and broader ACOG guidance confirm contraception is needed until menopause is confirmed.

In hypothalamic amenorrhea: Sporadic ovulation can resume before periods do, meaning pregnancy can occur before the first bleed.

In POI: Spontaneous ovulation and pregnancy occur in 5 to 10 percent of women with confirmed POI, so contraception is appropriate unless actively trying to conceive.

In lactational amenorrhea: As described above, LAM is only reliable before six months postpartum and only with exclusive breastfeeding. After that threshold, a separate contraceptive method should be in place.

Specific drug considerations in pregnancy: Dopamine agonists (cabergoline, bromocriptine) used for hyperprolactinemia are generally discontinued once pregnancy is confirmed, though bromocriptine has a longer safety record in early pregnancy if a macroprolactinoma requires continued treatment. Metformin for PCOS is often continued through the first trimester and sometimes beyond to reduce miscarriage risk, though ACOG Practice Bulletin 230 notes this is an evolving evidence base. Levothyroxine doses typically need a 25 to 30 percent increase in pregnancy to maintain maternal euthyroid status; thyroid function should be checked as soon as pregnancy is confirmed and every four weeks through 20 weeks.

Who This Is Right For, and Who It Is Not

Secondary amenorrhea workup is appropriate for you if:

• You have missed three or more periods and pregnancy is excluded
• Your cycles have always been irregular and this has never been investigated
• You are under 40 and experiencing symptoms suggesting low estrogen (hot flashes, bone pain, vaginal dryness)
• You are a competitive athlete or dancer with missing or infrequent periods
• You have signs of androgen excess alongside cycle changes

You may not need a full amenorrhea workup if:

• You are on a hormonal IUD, implant, Depo-Provera, or continuous combined pills (amenorrhea is expected)
• You are exclusively breastfeeding a baby under six months
• You missed one period following a major illness or extreme stress and it returned the following month

Caveats by life stage:

• Adolescents with primary amenorrhea should be referred to a specialist with experience in pediatric and adolescent gynecology. The differential includes chromosomal causes (Turner syndrome), Mullerian anomalies, and constitutional delay.
• Postmenopausal women with any bleeding should be evaluated for endometrial pathology before assuming a hormonal cause. This is not missed period territory; this is abnormal bleeding territory.