Anovulatory Cycles: Why They Happen and What to Do

You had what looked like a period, but your OPK never turned positive and your temperature never shifted. Now you are wondering whether the cycle "counted," and whether one anovulatory cycle means something is wrong. The honest answer is that anovulation is more common than most people realise, and what matters is the pattern across months, not what happened in any single cycle.

An anovulatory cycle is a menstrual cycle in which no egg is released. The lining of the uterus may still build and shed, so you may still bleed, but the central event of the cycle, ovulation, did not happen. In population data, up to one in four cycles in apparently healthy ovulating women under the age of 35 is anovulatory in any given year.⁴ In people with polycystic ovary syndrome (PCOS), the proportion is far higher, often 70 to 80 percent of cycles without treatment.¹ This post is the long, careful version of what an anovulatory cycle is, why it happens, how to recognise one, and when the pattern is worth a clinical conversation.

What an anovulatory cycle actually is

A typical ovulatory cycle has two halves divided by a single event. In the first half, the follicular phase, oestrogen rises as a dominant follicle grows. In the second half, the luteal phase, the empty follicle becomes the corpus luteum and produces progesterone. Progesterone stabilises the endometrial lining. If pregnancy does not occur, progesterone falls, the lining sheds, and the next cycle begins.

In an anovulatory cycle, no follicle ruptures. No egg is released. No corpus luteum forms. Progesterone never rises. Oestrogen alone continues to build the lining until either the oestrogen level dips on its own (oestrogen withdrawal bleeding) or the lining simply outgrows its blood supply and sloughs unevenly (oestrogen breakthrough bleeding). Either way, the bleed that follows is not a true menstrual period in the technical sense. It is anovulatory bleeding.

This distinction matters for two reasons. First, an anovulatory bleed is not predictable in timing the way a luteal-phase period is, because the corpus luteum was not there to set the clock. Second, prolonged exposure to oestrogen without the protective effect of progesterone is a small but real risk factor for endometrial overgrowth, particularly in PCOS where this pattern can go on for months.¹

When I am sitting with a patient who has just had one of these cycles, the first thing I want them to understand is that it is not a mistake their body made. It is a different kind of cycle. The fertility implication for that single cycle is straightforward, no egg means no chance of pregnancy that month. The longer-term implication is about pattern recognition, not panic.

How common is it, really

The 2013 BioCycle data, which followed apparently regular-cycling women prospectively with daily hormone sampling, found that around 8 to 11 percent of clinically regular cycles in healthy women under 35 were biochemically anovulatory.⁴ In other words, the cycle looked normal from the outside, but no ovulation actually occurred. In larger pooled estimates across age and reproductive status, the proportion rises to roughly one in four cycles per year.

In PCOS, the picture is different. The 2023 International Evidence-Based Guideline for PCOS defines anovulation in clinical terms as cycles longer than 35 days, fewer than eight cycles per year, or cycle-to-cycle variation greater than nine days.¹ Most untreated people with PCOS who have not yet been on hormonal contraception meet at least one of those criteria. In population studies of PCOS cohorts, 70 to 80 percent of cycles without treatment are anovulatory.

So the framing I want you to leave this section with is this: if you are reading this after one suspected anovulatory cycle and you do not have PCOS, you are probably looking at a normal-range event. If you have PCOS or suspect you might, this is more likely a feature of the syndrome that is worth tracking and discussing.

How to recognise an anovulatory cycle

The signals to look for fall into three groups: prospective signals that should appear before ovulation, retrospective signals that should appear after, and the character of the bleed itself.

On the prospective side, in an ovulatory cycle you would expect to see a positive ovulation predictor kit (OPK) somewhere in the expected window, followed within 24 to 36 hours by the surge resolving. In an anovulatory cycle, the LH line on the OPK either never reaches the test-line intensity, fluctuates without a clear peak, or, in PCOS, shows multiple "near positive" results over many days that never coordinate with a temperature shift. You may also notice egg-white cervical mucus (EWCM) appearing more than once across the cycle without a confirmed shift after, as the body attempts ovulation more than once.

Retrospectively, a true ovulatory cycle is confirmed by a sustained biphasic basal body temperature (BBT) pattern, typically at least three consecutive days at least 0.2°C (0.4°F) above the prior six-day average. In an anovulatory cycle, that shift does not happen. The chart looks flat, or wavers up and down without a sustained rise. If you are using a fertility-tracking app and it has never been able to confidently mark an ovulation day on your chart, that is meaningful information.

The bleed itself can also tip you off. Anovulatory bleeding is often lighter or heavier than your usual flow, shorter or longer, and arrives off-schedule, especially more than 35 days after the previous bleed. In PCOS, very heavy or prolonged bleeding after a long gap is a particular pattern to watch for, because it reflects an endometrium that has built up across many weeks of unopposed oestrogen.

If you want the lowest-effort recognition stack, it is this: daily OPK from cycle day eight onwards, daily BBT under consistent conditions, and a cervical-mucus check two or three times a day. When none of these three signals align across an entire cycle, the cycle is very likely anovulatory. I cover the multi-signal approach in more detail in how to tell if you're ovulating with PCOS.

Why anovulation happens

There is no single cause of anovulation. There are several categories of cause, and most readers fit into one or two of them.

Hormonal causes are the largest category. PCOS sits at the top of the list, and it is worth understanding the mechanism. In PCOS, an elevated LH:FSH ratio, alongside hyperandrogenism and frequently insulin resistance, disrupts the FSH pulse the brain produces in the early follicular phase. Many small antral follicles are recruited, but no single follicle is selected for dominance, and ovulation does not happen.¹ Other hormonal causes include hypothalamic dysfunction (often associated with low body weight, very high exercise loads, severe psychological stress, or a combination), hyperprolactinaemia, and thyroid dysfunction, both hyperthyroidism and hypothyroidism.⁵

Age-related anovulation rises in the late thirties and forties as the antral follicle count declines and follicular sensitivity to FSH changes. In the perimenopausal transition, anovulatory cycles become more common and more clustered.

Iatrogenic causes include the first few cycles after stopping hormonal contraception (especially long-acting injectables), the postpartum period, and the months following a pregnancy loss. Certain medications, including some psychotropics and chronic NSAID use around ovulation, can also disrupt ovulation.

Lifestyle and life-stage causes include significant weight loss or weight gain, severe sleep deprivation, eating disorders, and the chronic stress states that go with them. These are not moral failings. They are biology responding to a real signal that the body interprets as "not the right time."

The 2023 PCOS Guideline anovulation criteria, again, are cycles longer than 35 days, fewer than eight cycles per year, or cycle-to-cycle variation greater than nine days.¹ If you meet any of these criteria, the clinical conversation is about evaluating for cause, not waiting another six months.

What bleeding without ovulation looks like

People often ask me whether an anovulatory bleed will show up at the usual time. The honest answer is: it might, but it does not have to. Because the bleed is not anchored to a corpus luteum, the timing is unpredictable. You may bleed three weeks after the previous bleed, you may go 50 or 60 days, and the volume can range from spotting to flow that is heavier and longer than your usual period.

Anovulatory bleeding can also be confusing because it does not necessarily "reset" cycle day one in the textbook sense. Most clinicians count cycle day one from the first day of meaningful bleeding, regardless of whether ovulation preceded it, simply because that is the only landmark available.

The pattern that most concerns me clinically is heavy or prolonged bleeding in PCOS after a long stretch without a period. The endometrium has been exposed to oestrogen without progesterone for many weeks, sometimes months, and when it finally sheds it can do so unevenly and at volume. Endometrial hyperplasia, a build-up of the lining that can occasionally progress to atypia, is a recognised risk in people with PCOS who go long stretches without progesterone exposure.¹ If you have not had a period in 90 days outside pregnancy, please contact your clinician, even if you feel fine.

One anovulatory cycle versus a pattern

A single anovulatory cycle in someone with otherwise regular cycles is, in most cases, an unremarkable event. Common triggers include travel, an acute illness, the cycles immediately after stopping the pill or another hormonal contraceptive, a stressful month, or simply biological noise. It does not mean your fertility has changed. It does not mean the next cycle will also be anovulatory. It does not predict difficulty conceiving.

Two or more anovulatory cycles per year in someone who is trying to conceive starts to shift the conversation. Per the 2023 PCOS Guideline, this pattern, even without other features, warrants a clinical evaluation.¹ In people with no fertility goals, two anovulatory cycles per year may simply be tracked.

A PCOS pattern of chronic oligo-ovulation or anovulation is qualitatively different. Cycles run consistently longer than 35 days, the gap between bleeds is wide, and confirmation of ovulation by BBT or progesterone is intermittent or absent. This pattern meets the Rotterdam ovulatory criterion of PCOS and should be paired with hyperandrogenism (clinical or biochemical) and/or polycystic ovarian morphology on ultrasound for the diagnosis.¹ I dig into the cycle-length side of this picture in long cycles with PCOS.

If you are trying to conceive and have had two or more anovulatory cycles in the past 12 months, you do not need to wait the full 12-month "infertility" rule to be evaluated. That rule was written for couples with no known fertility factor, and documented anovulation is itself a known factor. I cover the exceptions in detail in when the year rule doesn't apply.

What to do this cycle if you suspect anovulation

If you are reading this in the middle of a cycle that does not look like it is going to ovulate, here is what I would tell you in clinic.

First, do not give up on the cycle until day 35 to 40 has passed. Late ovulation is common, and in PCOS it can happen as late as day 40, day 50, or beyond. A cycle without an obvious LH surge by day 17 is not yet an anovulatory cycle. The distinction between late ovulation and no ovulation matters, and I cover it in late ovulation: normal, concerning, or both.

Second, keep tracking. The most useful data in a possibly-anovulatory cycle is a complete BBT chart from cycle day one through to either the next period or day 45, whichever comes first. Continue cervical mucus observations daily. Continue OPK daily, or every other day if cost is an issue, throughout the extended window.

Third, if you have PCOS and have gone 60 days without a period, contact your clinician. A short course of an oral progestin (often medroxyprogesterone or micronised progesterone) can induce a withdrawal bleed and reset cycle day one. This is a small, safe intervention that protects the endometrium and gives you a clean starting point for the next cycle.

Fourth, do not start over-the-counter "fertility stacks" you saw advertised online without telling your clinician. Some of those supplements interact with the medications you may end up needing, and inositol in particular has dose and form considerations worth discussing properly.

When to call your clinician

The criteria below are not exhaustive, but if you tick any of them, the appointment is worth booking now rather than after another cycle.

• Cycles consistently longer than 35 days, or fewer than eight periods per calendar year (the 2023 PCOS Guideline anovulation criterion).¹
• No period for 90 days outside pregnancy.
• Bleeding that is heavy enough to soak through a pad every hour, or that lasts more than seven days, or that includes clots larger than a 50p coin or a US quarter.
• Trying to conceive for six months or more with documented anovulation in multiple cycles (the 2023 Guideline standard for PCOS).¹
• New onset of cycle irregularity in someone with previously regular cycles, especially with symptoms of thyroid dysfunction (cold intolerance, fatigue, weight change, palpitations) or hyperprolactinaemia (galactorrhoea, headache, visual changes).
• Age 35 or older and trying to conceive: ASRM recommends evaluation at six months rather than 12.³

If you are not trying to conceive but are seeing this pattern, you still deserve an evaluation. Long-term unopposed oestrogen exposure is not a benign issue.

What the workup usually includes

A standard anovulation workup looks similar across most clinics. The exact panel will vary, but the framework, drawn from the ASRM committee opinions on infertility evaluation and amenorrhoea evaluation, is consistent.³,⁵

A mid-luteal progesterone drawn seven days after suspected ovulation (often called a "day 21 progesterone" in a notional 28-day cycle) is the single most informative test. A level below 3 ng/mL strongly suggests no ovulation occurred in that cycle. A level above 10 ng/mL is reassuring confirmation. Numbers in between are real ovulation but with possibly marginal corpus luteum function. One low result is not a verdict; serial measurements across two or three cycles give the actual picture.

A baseline endocrine panel typically includes anti-Müllerian hormone (AMH), follicle-stimulating hormone (FSH), luteinising hormone (LH), and oestradiol on cycle day two to five. These give your clinician a picture of ovarian reserve and the FSH:LH balance.

Thyroid-stimulating hormone (TSH) and prolactin are routine, because both can produce anovulation as their primary fertility presentation, and both are easily treatable.

In a PCOS evaluation, androgens are added: total testosterone, free testosterone, sex hormone-binding globulin (SHBG), and dehydroepiandrosterone sulphate (DHEA-S). A transvaginal pelvic ultrasound assesses antral follicle count and ovarian morphology.

I cover the full workup in more detail in PCOS workup essentials.

Treatment paths if anovulation is confirmed

The treatment ladder depends on the cause. For people with PCOS who are trying to conceive and have documented anovulation, the 2023 Guideline ladder is reasonably clear.¹

Lifestyle changes come first where applicable. A modest five to ten percent change in body weight, where there is excess weight, has been shown to restore spontaneous ovulation in a meaningful proportion of people with PCOS, without medication. This is not framed as a moral imperative or a quick fix. It is one option that has supportive evidence, and it is the first conversation most guidelines want clinicians to have before moving to medication.

Letrozole is the first-line ovulation induction medication for PCOS, established by the 2014 PALO trial in the New England Journal of Medicine and reaffirmed by the 2023 Guideline.¹,² In PALO, letrozole produced higher ovulation rates per cycle (61.7 percent vs 48.3 percent) and a higher cumulative live-birth rate (27.5 percent vs 19.1 percent) compared with clomiphene over five cycles.²

Clomiphene citrate remains second-line for PCOS, although it is still in wide use.

Metformin may be added alongside letrozole in patients with documented insulin resistance, or used alone in selected patients who prefer to delay ovulation-induction medications.

Inositol (specifically myo-inositol and D-chiro-inositol in a 40:1 ratio) has some evidence in PCOS as a pre-treatment or adjunct, though the evidence base is weaker than letrozole. It is a reasonable option for someone who is not yet on prescription medication and wants to try a supplement-based approach for two to three cycles first.

If anovulation is caused by hypothalamic dysfunction, thyroid disease, or hyperprolactinaemia, treatment is directed at the underlying cause, and ovulation often returns once that is addressed.

I cover the letrozole pathway in detail in letrozole for PCOS overview.

What is normal, what is a flag

Normal: an occasional anovulatory cycle, especially after travel, illness, a course of antibiotics that disrupted gut absorption of the pill, a stressful event, or in the months after stopping hormonal contraception. One anovulatory cycle per year in someone otherwise regular is not a clinical concern.

Worth discussing: more than two anovulatory cycles in a 12-month TTC attempt, any PCOS pattern of chronic oligo-ovulation, new onset of irregular cycles in someone previously regular, or anovulation in someone aged 35 or older who is trying to conceive.

Red flag: bleeding heavy enough to require changing a pad every hour, bleeding lasting more than seven days, clots larger than a 50p coin or US quarter, severe pelvic pain, no period for more than 90 days outside pregnancy, or any sign of pregnancy complication on top of an irregular bleed.

What you can do tonight

If you are at the end of a cycle that did not seem to ovulate, this is a small list of practical actions.

1. Open your tracking app or calendar and write down the actual signals from this cycle: any positive OPK day, any BBT shift day, any peak EWCM day, and the days of any bleeding. The pattern across three cycles will be more useful to your clinician than a single chart.
2. If you have PCOS and your last period was more than 60 days ago, book a clinical appointment this week. A progestin to induce a withdrawal bleed is a small intervention and worth doing rather than waiting another month.
3. If you are trying to conceive and meet any of the earlier-evaluation criteria above (PCOS, age 35+, two or more anovulatory cycles in 12 months), book an evaluation rather than waiting for the full 12-month rule.
4. If you are not trying to conceive but the pattern is new, the same evaluation is still worth having. Unopposed oestrogen exposure is a long-term consideration, not just a fertility one.
5. Resist the urge to start a stack of over-the-counter supplements before that appointment. Bring the questions, not the supplements, to the visit.

What's next

• If this is your first noticed anovulatory cycle and you want to learn the multi-signal recognition method: how to tell if you're ovulating with PCOS
• If your ovulation seems late rather than absent: late ovulation: normal, concerning, or both
• If your cycles run consistently longer than 35 days: long cycles with PCOS
• If you have been trying for six months or more with documented anovulation: when the year rule doesn't apply and letrozole for PCOS overview
• If this cycle hit harder than you expected: when a cycle doesn't work

Sources

1. Teede HJ, Tay CT, Laven JJE, et al. Recommendations from the 2023 International Evidence-Based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Fertility and Sterility 2023;120(4):767-793. https://doi.org/10.1016/j.fertnstert.2023.07.025
2. Legro RS, Brzyski RG, Diamond MP, et al. Letrozole versus clomiphene for infertility in the polycystic ovary syndrome. New England Journal of Medicine 2014;371(2):119-129. https://www.nejm.org/doi/full/10.1056/NEJMoa1313517
3. Practice Committee of the American Society for Reproductive Medicine. Diagnostic evaluation of the infertile female: a committee opinion. Fertility and Sterility 2015;103(6):e44-e50. https://doi.org/10.1016/j.fertnstert.2015.03.019
4. Hambridge HL, Mumford SL, Mattison DR, et al. The influence of sporadic anovulation on hormone levels in ovulatory cycles. Human Reproduction 2013;28(6):1687-1694. https://doi.org/10.1093/humrep/det090
5. Practice Committee of the American Society for Reproductive Medicine. Current evaluation of amenorrhea. Fertility and Sterility 2008;90(5 Suppl):S219-S225. https://doi.org/10.1016/j.fertnstert.2008.08.038