Possible Causes of Abnormal Periods

Causes of abnormal periods

Verywell / Cindy Chung 

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 may be normal to have once in a while, it's undoubtedly stressful. Understanding what could be going on in your body to cause the irregularity can help.

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 could mean different things.

A normal menstrual cycle lasts between 21 and 35 days. You may have spotting, bleeding, or a combination for three to seven days, on average.

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.

In an abnormal cycle, your period could be longer or shorter or may come earlier or later than anticipated. It may be different in the amount of flow. You may also find that it stops and starts, even if overall it lasts the same number of days. You might experience bleeding in between your periods when you would normally not expect bleeding. You might have more cramping than you normally have for your cycle. Basically, anything that isn't what you would expect is abnormal and should be watched.


There are a number of things that cause your period to be different, many of which are simple changes to your daily routine. Keep these reasons in mind so that you can pay closer attention to them when trying to pinpoint a reason for your abnormal period.

  • Stress: Stress can wreak all sorts of havoc on your body. The stress hormones can cause your cycle to be delayed or even stop. Many women notice that when they experience great stress—for whatever reason, be it final exams, moving, a death in the family, or financial hardship—they have periods that are not normal in timing and length. In some cases, they may even skip a period.
  • Increased or decreased exercise: 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. This is especially true if it is accompanied by a large or rapid weight loss, since having a normal period is tied to having a certain amount of body fat.
  • Change in sleep patterns: Your sleep patterns alter your cycle. When you have a sleep pattern disruption—say you go from working days to working nights—your hormones are altered. This alone can be enough to disrupt your cycles. While this might not last very long, if you find a stable routine, it can be an ongoing problem when you have a schedule that frequently has you mixing up your days and nights.
  • New medications: Anything you take has the potential to interrupt your cycle. This is particularly true of medications that alter your hormones in any way—for example, birth control. While this may seem obvious, many people do not think about this because they are taking the medications for reasons other than birth control. Sometimes it just takes your body a while to figure things out before finding its new normal. Perhaps it was a medication that helped alleviate a problem that was causing your period to be abnormal and now that it's regulated, the change feels abnormal. This is where good communications with your doctor or midwife is helpful.
  • Illness: When you are not well your body can behave in different ways. For example, if you have thyroid disease, your hormones might not be working effectively, which would cause your cycles to be abnormal. Getting this condition under control and getting your thyroid levels back to normal will help stabilize your periods and enable you to get into a normal pattern.

When to See Your Doctor or Midwife

The best thing to do is to take a pregnancy test if you think your period was weird. If it's negative, wait for your next period. If it is also weird, consider seeing your doctor or midwife for an exam to help get to the bottom of the cause of your abnormal period.

You should call your doctor or midwife any time you have a question about your menstrual cycle. This is particularly true if you are trying to get pregnant and notice that your cycle length is shorter than 25 days.

You may also want to seek advice if you have erratic cycle lengths, or if you are under 35 years old and have been trying to conceive for over a year. If you are over 35, the recommendation is that you wait no more than six months.


Your doctor will start by taking a comprehensive medical history that includes information about your menstrual cycles, including when you started having periods. She will use this information to consider what testing should be done. Testing can take several different forms but often starts with blood work to measure your hormones and diagnose conditions like thyroid disease.

You may also have a vaginal exam. This will include swabs to test for infections that may be altering your cycles, as well as to identify anything that is going on structurally. Your doctor may order a vaginal ultrasound. This will 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

For many women, pregnancy is top of mind as the reason for an abnormal period. Though it certainly is a possibility, it may not be the most likely scenario for you based on your sex life and use of birth control.

For example, a woman who has taken her birth control pills regularly and has not missed any days, nor had a medication change that would alter her birth control status, may still have a period that is lighter or shorter. The abnormal period is more likely simply a result of less build up in her endometrium (uterine lining). Pregnancy could be an option, but it isn't the most likely option.

Vaginal Bleeding in Pregnancy

Some pregnant women experience bleeding and think that it is their period, but that isn't always the case. For example, the bleeding could be implantation bleeding, which occurs around the time the fertilized egg is burrowing into your endometrium. This may look like spotting and confuse someone into thinking they had a really light period until a second missed period suggests pregnancy.

A woman may also bleed during pregnancy because something is going on. This might be a hormonal issue or impending miscarriage that requires you to get care from a doctor or midwife.

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 be tested for abnormal periods and find a treatment that helps get your period back on track.

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