Possible Causes of Abnormal Periods

Causes of abnormal periods

Verywell / Cindy Chung 

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You know your period. You know when to expect it and how to calculate the number of pads or tampons you will need. You probably even know what you can get away with wearing in terms of clothes, based on your flow. It's likely that you would know if your period were abnormal in any way.

While an abnormal period can be normal to have once in a while, it's undoubtedly stressful. It can help to understand what could be going on in your body to cause the irregularity in your menstrual cycle.

What Is an Abnormal Cycle?

A period that is abnormal is one that is in some way different from a typical, normal period—but this can mean different things for different people.

A normal menstrual cycle lasts between 21 and 35 days. On average, you might have spotting or bleeding (or a combination) for three to seven days.

Your cycles will typically look very similar. If you normally have periods with three days of spotting and two days of bleeding, an abnormal period might only be two days of spotting and no bleeding.

During an abnormal cycle, your period could be longer or shorter than usual. It also might come earlier or later than anticipated. It could also differ in the amount of flow you have. Your flow might also stop and start but still last the same number of days overall.

You might experience bleeding in between your periods when you would normally not expect to bleed. You might also have more cramping than you normally do.

When it comes to your period pay attention to anything that does not feel or look like whatever "typical," "usual," or "normal" means for you.


There are a number of reasons your period might be different than what is typical for you. Many causes of abnormal periods are related to simple changes to your daily routine, while others could be a sign of a more serious issue that needs your (and your doctor's) attention.


If you are sexually active and your period seems off, first check to see if you are pregnant. It might seem obvious but if you were not trying to conceive, are on birth control, have certain health conditions, or have not had other signs or symptoms of pregnancy, it won't necessarily be your first assumption if your period is late or off.

Feeling Stressed

Stress can wreak havoc on your body. Stress hormones can cause your cycle to be delayed or even stop. If you experience great stress (be it final exams, moving, a death in the family, or financial hardship) your periods might be abnormal in timing and length. In some cases, you might even skip a period.

Changing Exercise Habits

Regular exercise is a great way to stay in shape and it is key to having a healthy body. Sometimes starting a new, intense, workout routine can cause your periods to be delayed or skipped.

Abnormal menstrual cycles related to increased physical activity are especially likely if it is accompanied by large or rapid weight loss. Having a regular period is tied to body fat. If you don't have enough, you might lose your period altogether.

Starting New Medications

Anything you take has the potential to interrupt your cycle—including prescription and over-the-counter (OTC) medications. It's especially true of a drug that alters your hormones, such as birth control.

People take or use birth control for many reasons that are not related to preventing pregnancy. They can also take medication for reasons that do not have to do with their reproductive health but can have an effect on it.

For example, if you are taking a medication to treat a condition that was causing your periods to be abnormal and the treatment helps to regulate your cycle, the change might feel abnormal to you.

If you are taking medication, your doctor or midwife can help you understand if it could affect your menstrual cycle.

Changing Sleep Patterns

Your sleep pattern can also alter your menstrual cycle. When you have a sleep pattern disruption (for example, if you go from working days to working nights) it changes your hormones. This alone can be enough to disrupt your cycles.

The interruption might not last very long if you are able to find a stable routine. It can become an ongoing problem if you have a schedule that has you frequently mixing up day and night.


When you are not well, it can change your physical and mental wellbeing in many ways. With regard to your menstrual cycle, certain medical conditions can cause changes to your periods.

For example, if you have thyroid disease it can cause your hormones to not work as well. This, in turn, can cause your menstrual cycle to become abnormal. However, if you get treatment for your thyroid condition and manage it effectively, it will help to stabilize your periods.

When to Call Your Doctor or Midwife

If your period seems weird or off in any way, the first thing to do is take a pregnancy test. If it is negative, wait to see how your next period goes. If you have another period that feels or seems off, it might be time to make an appointment with your doctor or midwife.

They can perform an exam to figure out what is causing the irregularities in your cycle and answer any questions you have about your menstrual cycle.

There are certain situations where it can be especially helpful to seek the advice of your doctor or midwife, such as:


Your doctor will take a comprehensive medical history that includes information about your menstrual cycles. They will likely start by asking you when you started having periods. Your doctor can use this information to consider what testing might be necessary or helpful.

Testing can take different forms but often starts with blood work. Lab tests can measure your hormones and also help your doctor diagnose conditions that can cause menstrual irregularities, such as thyroid disease.

You might also need to have a vaginal exam. Your doctor will take swabs to test for infections that could be altering your cycle, as well as to identify any structural issues.

Your doctor may want to order a vaginal ultrasound to screen for cysts or fibroids in your uterus or on your ovaries.

You may also be asked to have an endometrial biopsy. This is where a small sample is taken from the liming of your uterus. It is only slightly more uncomfortable than a regular pelvic exam.

Pregnancy and Abnormal Periods

If your period is late or you skip a period, pregnancy might be at the top of your mind as a reason. While it's certainly a possibility, it's not always the most likely explanation.

For example, a woman who has taken her birth control pills regularly and has not missed any dose and has not had any medication change that would alter her birth control status could still have a period that is lighter or shorter.

In this example, having an abnormal period is more likely a result of less build-up in the endometrium (uterine lining). Pregnancy could still be a cause of the change to her period, but it is not the only (or even the most likely) cause in this situation.

Vaginal Bleeding in Pregnancy

Pregnant women can experience bleeding and mistake it for their period. There are several reasons for bleeding in pregnancy that you should be aware of.

Abnormal bleeding could be implantation bleeding, which occurs around the time the fertilized egg is burrowing into the endometrium.

Implantation bleeding may look like spotting. It can easily confuse someone into thinking they had a really light period (until a second missed period suggests that they could be pregnant).

You can also bleed during pregnancy for other reasons—some of which can be serious. You could have an underlying health condition that needs treatment, such as a hormonal issue, an impending miscarriage, or an ectopic pregnancy.

A Word From Verywell

Tracking your period is a great way to identify when your period is longer or shorter, your bleeding is heavier or lighter, or if you skip periods altogether. These are signs that you might have an abnormal period. Working with your doctor, you can quickly get tested for abnormal periods and find a treatment that helps get your period back on track.

Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.