Irregular Periods: Causes and When to Worry

A little unpredictability in your cycle is normal, and often it’s just your body responding to something ordinary, like stress, a new medication, poor sleep, the first couple of years after your first period, or the years leading into menopause. Doctors consider a cycle irregular when it falls outside 24 to 38 days apart, when bleeding lasts longer than 7 days, or when the pattern itself feels unpredictable from month to month.¹²

On this page

1. What does a normal period actually look like?
2. What’s normal at different life stages?
3. How are the causes of irregular periods classified now?
4. What’s actually behind an irregular period?
5. What can untreated irregular periods do over time?
6. Can you still get pregnant with irregular periods?
7. Getting to a diagnosis
8. What are the treatment options?
9. When to see a doctor?

What does a normal period actually look like?

For most adults, a typical menstrual cycle, counting from day one of one period to the first day of the next, falls between 24 and 38 days. The bleeding usually lasts 2 to 7 days, and total blood loss over one period is between 5 and 80 milliliters, or roughly one to five tablespoons.¹ You may also see a 21-to-35-day range in older sources; 24 to 38 days is the range doctors currently use to define abnormal bleeding. This is often measured by how often you had to change your pad, tampon, or menstrual cup/disk.

What’s normal at different life stages?

At teenage

If you’re a teenager, the range is naturally wider. In the first few years after menarche (the medical term for when periods start), it’s common for cycles to range from 21 to 45 days, last up to 7 days, and require changing a pad or tampon 3 to 6 times a day.³⁴ This is because the communication between your brain and your ovaries is not properly established yet. This is known as the hypothalamic-pituitary-ovarian axis; by about the third year after your first period, roughly 60% to 80% of cycles settle into the 21-to-34-day adult range on their own.³

If you’re a parent or caretaker and a teenager mentioned irregular periods, some irregularity in the first and third year is expected. However, if something feels extremely off, consult an OB-GYN right away.

The American College of Obstetricians and Gynecologists, the leading US professional body for women’s health, recommends that clinicians ask about a teenager’s period at every checkup, treating it like a vital sign, the same way they’d check blood pressure or pulse.³ That’s a good habit to borrow at home too. Keeping a simple record of dates, flow, and any pain makes it much easier to identify any irregularity; using a period tracker is fairly easy and convenient.

Perimenopause

Perimenopause is the transition into menopause, and irregular periods are usually the first sign it’s begun. It typically starts in your 40s (occasionally as early as your mid-30s) and lasts an average of four years, though the timeline varies person to person.⁵⁶ Cycles may start arriving closer together or further apart, and flow can feel lighter or heavier than what you’re used to. This is a normal part of estrogen and progesterone naturally shifting as ovulation becomes less frequent⁶; it’s not usually a sign that something’s wrong.

Still, it is important to check in with your OB-GYN if bleeding feels unusually heavy, happens after sex, or shows up again after a full year without a period.⁷

How are the causes of irregular periods classified now?

For a long time, doctors described period problems with a set of Latin-rooted terms, and you’ll still come across these in older articles and forums.⁸⁹

• Amenorrhea: Periods have stopped completely.
  • Primary amenorrhea is when a period hasn’t started by age 15 despite normal development.
  • Secondary amenorrhea is no period for 3 months in someone whose cycles were previously regular, or 6 months in someone whose cycles were previously irregular.
• Oligomenorrhea: Infrequent periods, typically fewer than nine cycles a year or cycles longer than 35 days.
• Polymenorrhea: Periods that come too often, with cycles shorter than 21 days.
• Menorrhagia: Heavy or prolonged bleeding during a period.
• Metrorrhagia: Irregular bleeding or spotting between periods.

In 2011, the International Federation of Gynecology and Obstetrics (FIGO) introduced a clearer system, and ACOG has been using it across the US since then.⁸¹⁰ The new umbrella term is abnormal uterine bleeding (AUB): any uterine bleeding that is abnormal in frequency, regularity, duration, or volume, outside of pregnancy.⁹ Causes are then sorted under one acronym, PALM-COEIN.⁸

PALM

Covers structural causes, things a scan or biopsy can detect.

• A polyp is a small benign growth.
• Adenomyosis is uterine-lining tissue growing into the uterine muscle wall.
• Leiomyoma, more commonly called a fibroid, is a noncancerous muscle growth in the uterus.
• Malignancy or hyperplasia refers to uterine cancer or an overgrown uterine lining, both uncommon but important to rule out.

COEIN

Covers the causes that aren’t structural.

• Coagulopathy is a blood-clotting disorder, such as von Willebrand disease.
• Ovulatory dysfunction means irregular or absent ovulation, the release of an egg from the ovary, and it’s the most common cause overall.
• Endometrial refers to a problem local to the uterine lining itself.
• Iatrogenic means caused by a medication or medical device, such as certain birth control methods or blood thinners.
• Not otherwise classified refers to any cause that doesn’t fit anywhere else.

What’s actually behind an irregular period?

Honestly? A lot of things, ranging from completely benign to ones that need real treatment. Here’s a breakdown:

Life stage

In the first year or two after your first period, cycles are often irregular because the brain-ovary connection is still maturing. The same happens during perimenopause, the years before menopause, when estrogen and progesterone naturally fluctuate, causing the periods to become shorter, longer, heavier, lighter, or stop altogether.⁵⁶⁷ Pregnancy stops periods entirely; unexpected bleeding when pregnancy is possible should be addressed immediately.

Hormones and underlying conditions

PCOS (Polycystic Ovary Syndrome) now known as PMOS (Polyendocrine Metabolic Ovarian Syndrome),¹¹¹² thyroid disorders, (Primary Ovarian Insufficiency) POI (when the ovaries stop working normally before age 40), structural issues like polyps or fibroids, endometriosis, pelvic inflammatory disease, uncontrolled diabetes, bleeding disorders like von Willebrand disease,⁴ eating disorders, and, rarely, uterine or ovarian cancer can all disrupt your cycle. If any of this sounds familiar, reach out to your physician; asking for help is a strength, not a failure.

Medications and birth control

Hormonal birth control commonly causes spotting in the first few months, which is often harmless. Certain other medications, including some antipsychotics, anti-seizure drugs, blood thinners, and steroids, can affect your cycle too.

Sexually transmitted infections

Certain infections can also cause irregular periods. Chlamydia and gonorrhea can inflame the cervix, often causing bleeding between periods or after sex. These infections don’t always come with other symptoms, so testing is the only way to know for sure and both can be successfully treated once diagnosed.¹³

Everyday life

Stress, rapid weight changes, intense exercise, poor sleep, and inconsistent nutrition can all throw off the hormonal signals that keep your cycle regular. None of this means you’re doing something wrong.¹⁴

What can untreated irregular periods do over time?

Occasional irregularities rarely cause lasting harm. But when heavy, prolonged, or absent periods continue for months without any treatment, a few things can happen quietly in the background.

• Ongoing heavy or prolonged bleeding can lead to iron-deficiency anemia, showing up as fatigue, dizziness, or shortness of breath.¹⁵
• Irregular or absent ovulation, common in PMOS and other hormonal imbalances, can make conceiving harder until the cause is treated.
• Estrogen also helps protect bone density, so conditions that lower estrogen for a long duration, like primary ovarian insufficiency or prolonged amenorrhea, can raise the risk of weaker bones over time.
• When ovulation doesn’t happen regularly, the uterine lining can build up without its usual monthly shedding, which can raise the risk of changes in the lining, a condition called endometrial hyperplasia.¹ This needs regular monitoring.

Can you still get pregnant with irregular periods?

If you’re planning to conceive, irregular cycles can make timing trickier, mainly because they make it harder to predict ovulation and pinpoint your fertile window. Conditions like PMOS or thyroid disorders can also reduce how often ovulation happens at all, which lowers the number of chances for conception across a year. If you do become pregnant with irregular periods, your care team may rely more on ultrasound dating than your last period date to track how far along you are.

None of this means pregnancy isn’t possible. For a majority of people with irregular periods, it is. It usually just means an appointment with your doctor or a fertility specialist can help you understand your particular pattern and provide support, if needed.

Getting to a diagnosis

Your doctor will likely ask about your cycle history, family history, medications, stress levels, weight changes, and any other symptoms. Based on your history, they may recommend:

• Pregnancy test: Your doctor will first rule out pregnancy.
• Blood tests: Checking hormones like TSH (thyroid-stimulating hormone), prolactin, FSH and LH (follicle-stimulating and luteinizing hormone, which drive ovulation), and testosterone, plus a complete blood count to check for anemia.¹⁶
• Pelvic ultrasound: A non-invasive imaging test that can spot fibroids, polyps, or ovarian cysts; in teenagers, structural causes are rare, so ACOG states that a routine ultrasound often isn’t necessary unless symptoms don’t improve with initial treatment.⁴
• Endometrial biopsy: A small tissue sample from the uterine lining, recommended at age 45+, or under 45 with risk factors (unopposed estrogen exposure, obesity, PMOS, persistent bleeding, failed medical management)
• Hysteroscopy: A thin, lighted scope used to look inside the uterus directly, typically used when imaging suggests a polyp or fibroid that needs closer evaluation or removal.

What are the treatment options?

Treatment depends entirely on the cause.

Lifestyle changes

Maintaining a healthy weight, a balanced diet, moderate exercise, consistent sleep, and stress management, especially for lifestyle- or weight-related causes.

Hormonal therapy

Birth control pills, the patch, the ring, or progestin-only options like pills, injections, or a hormonal IUD, to regulate cycles and reduce heavy bleeding.

Targeted medications

• The levonorgestrel IUD (Mirena, Liletta) is first-line medical therapy for heavy menstrual bleeding
• Two oral combination medications, Oriahnn (elagolix, estradiol, norethindrone acetate), approved in 2020, and Myfembree (relugolix, estradiol, norethindrone acetate), approved in 2021, are FDA-approved specifically for heavy menstrual bleeding caused by uterine fibroids, for use up to 24 months¹⁷¹⁸
• Tranexamic acid for heavy bleeding
• NSAIDs (ibuprofen, naproxen), which are a first step for mild to moderate heavy bleeding¹⁹
• Antibiotics for pelvic inflammatory disease
• Thyroid medication for a thyroid disorder²⁰
• In case of anemia, your doctor may prescribe oral or intravenous iron, alongside addressing the cause

Procedures for structural causes

• Myomectomy (removes fibroids)
• Dilation and Curettage (D&C) (removes lining tissue)
• Endometrial ablation (removes the lining)
• Hysterectomy (removes the uterus), usually a last resort

When to see a doctor?

Some irregularities are simply due to minor lifestyle changes. Reach out to a doctor if you notice:

• An unexplained change in a previously regular cycle
• Cycles shorter than 24 days or longer than 38 days as an adult (or shorter than 21 or longer than 45 as a teenager)¹⁴
• Bleeding that lasts more than 7 days, or having to change a pad or tampon hourly
• No period for three months or more, without pregnancy, breastfeeding, or menopause
• Bleeding between periods or after sex
• Severe pain with nausea or vomiting
• Any bleeding after menopause is confirmed (12 months period-free)⁷
• Signs of anemia: fatigue, dizziness, shortness of breath
• Trouble conceiving after months of trying, with irregular cycles

If you’re a teenager and experience any of this or something else entirely, it’s completely reasonable to keep your parents or caretaker in the loop. And equally reasonable to ask for privacy with your OB-GYN if that feels comfortable.

Frequently asked questions