What Does An Irregular Period Mean About My Fertility?

Your period can tell you a lot about your reproductive health—so when it’s irregular, it’s normal to wonder what that means for your fertility. The good news? An irregular cycle doesn’t automatically mean something’s wrong. But it can be a signal worth paying attention to, especially if you’re thinking about freezing your eggs or trying to conceive in the future.

Let’s break down what “irregular” really means, what might cause it, and how it may or may not impact your fertility.

First, what counts as an irregular period?

A textbook menstrual cycle is 28 days, but plenty of people fall outside that exact window. In general, a cycle is considered regular if:

• It occurs every 21–35 days
• Bleeding lasts about 2–7 days
• The pattern is relatively consistent month to month

When people say they have “irregular periods,” they might be describing a wide range of experiences. Medically, irregular menstruation can take several forms, each with its own terminology:

• Amenorrhea (ey-men-uh-REE-uh): When your period stops for at least three months and you're not pregnant or on birth control.
• Oligomenorrhea (ol-i-goh-men-uh-REE-uh): Infrequent periods, typically occurring more than 35 days apart.
• Polymenorrhea (pol-ee-men-uh-REE-uh): Frequent periods that occur less than 21 days apart.
• Menorrhagia (men-uh-REY-jee-uh): Very heavy periods—also known as excessive menstrual bleeding. This is different from anovulatory bleeding (bleeding without ovulation), even though the two are sometimes confused.
• Prolonged menstrual bleeding: Periods that last more than 8 days on a regular basis.
• Shortened menstrual bleeding: Periods that consistently last less than 2 days.
• Dysmenorrhea (dis-men-uh-REE-uh): Painful periods, often involving severe menstrual cramps.
• Intermenstrual bleeding: Spotting or bleeding that occurs between periods.
• Cycle variability: When your cycle length changes dramatically month to month, typically a variation of more than 20 days between your shortest and longest cycle.

Some of these patterns may be temporary or benign. Others may suggest that ovulation isn’t happening regularly, which can impact your ability to conceive or be a sign of an underlying condition like PCOS, a thyroid issue, or hormone imbalance.

Why ovulation still matters—even if you’re not trying to conceive right now

When your menstrual cycle is irregular, it often means that ovulation isn’t happening on a predictable schedule—or may not be happening at all. While you may not be trying to get pregnant right now, ovulation is still an important marker of how your reproductive system is functioning.

Ovulation is the process of releasing an egg from your ovary, typically once per cycle. If it’s not happening regularly, it could be a sign of a hormonal imbalance, conditions like PCOS, or other issues.

Irregular periods are common

You're not alone if your cycle doesn't run like clockwork. In fact, about 14% to 25% of women experience irregular menstrual cycles. This can mean that cycles are shorter or longer than average, the flow is unusually heavy or light, or that periods come with other symptoms like significant abdominal cramping. While some variation is completely normal, consistently irregular cycles, especially when paired with other symptoms, can sometimes signal an underlying issue worth discussing with a doctor.

What causes irregular periods?

There are a range of potential causes, and many of them are treatable. Some common reasons include:

• Polycystic ovary syndrome (PCOS): A common hormonal condition that affects ovulation. PCOS is one of the most frequent causes of irregular periods and infertility, but it’s also highly manageable with the right care.
• Thyroid disorders: Both hyperthyroidism and hypothyroidism can disrupt menstrual cycles and hormone balance.
• High levels of stress: Chronic stress can impact the hypothalamus (a part of your brain that regulates hormones), leading to missed or delayed periods.
• Excessive exercise or very low body fat: Athletes or those with low BMI may experience missed periods due to disruptions in hormone production.
• Endometriosis: A condition where tissue similar to the uterine lining grows outside the uterus, which can interfere with your cycle and cause painful periods.
• Uterine fibroids: Noncancerous growths in the uterus that can lead to heavy, prolonged, or unpredictable bleeding.
• Pelvic Inflammatory Disease (PID): An infection of the reproductive organs that can cause inflammation, scarring, and irregular bleeding.
• Certain medications: Including antipsychotics, chemotherapy drugs, and others that may interfere with hormone levels.
• Hormonal birth control: While many types of birth control regulate periods, some—like the contraceptive pill, IUD (coil), implant, or contraceptive patch—can cause irregular bleeding or even stop your period altogether.
• Perimenopause: In your late 30s and 40s, hormone levels begin to shift, often causing cycles to become less predictable.
• High prolactin levels: Sometimes caused by medications or pituitary issues, this hormone imbalance can affect ovulation and cycles.
• Pregnancy: It might seem obvious, but pregnancy is a common reason for a missed period—and often the first one that should be ruled out.

How irregular periods affect egg freezing

If you’re considering freezing your eggs, an irregular cycle doesn’t necessarily disqualify you. But it might make early fertility testing and planning even more important.

One of the key hormones used to assess fertility is anti-Müllerian hormone (AMH), which gives insight into your ovarian reserve—how many eggs you have left. An irregular cycle doesn’t always correlate with a low AMH, but in some cases (like with PCOS), AMH can actually be elevated.

If you're not ovulating consistently, your doctor may adjust your medication protocol or monitoring strategy during an egg freezing cycle to make sure it’s effective and safe. In fact, for some people with irregular cycles, egg freezing may be especially empowering—allowing you to preserve your eggs while figuring out what’s going on hormonally.

What does a long cycle mean?

If your cycle regularly stretches beyond 38 days, it’s considered long (or “infrequent menstruation”). This could mean that ovulation is happening later than usual—or in some cases, not at all. Conditions like PCOS or hypothyroidism are common culprits, both of which can interfere with regular ovulation.

Long cycles may result in fewer ovulatory events over time, which can impact your chances of conception if you’re trying to get pregnant unassisted. That said, having a long cycle doesn’t automatically mean you’re infertile. Some people with longer cycles still ovulate consistently, just on a different schedule.

When it comes to egg freezing, a longer cycle may influence the timing of your stimulation protocol, but doesn’t necessarily affect your ovarian reserve or how many eggs you can retrieve. Your doctor may monitor your hormones more closely or adjust your medication plan to sync things up.

What does a short cycle mean?

Cycles shorter than 24 days are considered short (or “frequent menstruation”) and may indicate that ovulation is happening too early, or not at all. In some cases, short cycles can signal a shortened follicular phase (the time between your period and ovulation), which may affect the quality of the egg released.

Short cycles can sometimes be linked to hormone imbalances, stress, perimenopause, or conditions like endometriosis. They don’t always mean your fertility is compromised, but they’re worth discussing with your doctor, especially if you’re seeing other symptoms like spotting, heavy bleeding, or severe cramping.

For egg freezing, short cycles may influence your monitoring schedule or how your doctor times your retrieval. As with long cycles, personalized care and hormone tracking can help ensure the process is effective, regardless of where your cycle falls on the calendar.

When to see a doctor

Consider seeing a fertility specialist or OBGYN if:

• You’ve had irregular cycles for more than 6 months
• You’re thinking about freezing your eggs and want to understand your cycle better
• You’re under 35 and have been trying to conceive for over a year, or over 35 and trying for six months
• You’re experiencing other symptoms, like acne, hair loss, weight changes, or pelvic pain

A few simple blood tests and an ultrasound can reveal a lot about what’s going on and help you make informed decisions about your reproductive health.

The bottom line

An irregular period doesn’t automatically mean something’s wrong with your fertility, but it’s worth paying attention to. It could be a signal that your hormones are out of sync or that ovulation isn’t happening consistently. Fortunately, most causes of irregular periods are manageable, and with the right support, many people go on to conceive or preserve their fertility successfully.

If you’re considering egg freezing and have irregular cycles, Cofertility can help you get clarity. Whether you’re looking to take control of your fertility now or just want to understand your options, we’re here to support you, no matter what your cycle looks like.

Freeze your eggs with Cofertility

We’d love the opportunity to support you on your egg freezing journey.

Through our Split program, qualified freezers can freeze their eggs for free when donating half of the eggs retrieved to a family who can’t otherwise conceive.

Through our Keep program—where you keep 100% of eggs retrieved for your own future use—we offer exclusive discounts on expenses, such as frozen egg storage. Keep members also still gain free access to our Freeze by Co Community, a safe space for those engaging in the egg freezing process (or gearing up for it) to connect and lean on each other.

By making egg freezing easier and more accessible, our programs further strengthen the American Society of Reproductive Medicine (ASRM)’s Committee Opinion that egg freezing can help promote social justice and strengthen gender equality.