Breakthrough bleeding is any bleeding or spotting you may experience between your normal menstrual periods or during pregnancy. It’s important to pay attention to any changes in your normal bleeding patterns from month to month. Women who smoke, for example, risk experiencing breakthrough bleeding.

Here’s more about how to identify breakthrough bleeding or spotting, what might be causing it, and when to see your doctor.

The typical menstrual cycle is 28 days long. Some cycles may be as short as 21 days, while others may be 35 days or more days in length.

Generally speaking, day one starts with the onset of your period and last around five days. After that, the hormones in your body gear up to produce an egg that may or may not be fertilized when you ovulate around day 14 of your cycle.

If the egg is fertilized, it may result in pregnancy. If not, your hormones will again adjust to shed the lining of your uterus and result in another period for around five days. Women generally lose around 2 to 3 tablespoons of blood during a menstrual period. Periods tend to be longer and heavier in teens and women nearing menopause.

Breakthrough bleeding is any bleeding that occurs outside of the normal menstrual period. This could be full-on bleeding — blood loss that’s enough to warrant a tampon or pad — or spotting.

There are many different reasons why you might experience bleeding between periods. It can be caused by anything from your body’s adjustment to hormonal contraception to miscarriage. Although some cases of bleeding may resolve on their own without treatment, it’s a good idea to report any changes to your doctor.

Bleeding between cycles is likely when you’re taking hormonal birth control pills or using other contraceptives, like an intrauterine device (IUD). It’s especially likely in the first few months after you start a new contraceptive or if you’re taking continuous and extended-cycle varieties, like ethinyl-estradiol-levonorgestrel (Seasonique, Quartette).

Doctors don’t know what exactly causes breakthrough bleeding while on traditional birth control pills. Some believe that it’s your body’s way of adjusting to the hormones.

Regardless, you may experience more breakthrough bleeding if you:

  • miss pills throughout your cycle
  • start any new medications or supplements while on the pill
  • experience persistent vomiting or diarrhea, which can affect your body’s absorption of the hormones

With extended or continuous birth control pills, you take active pills throughout the entire month to effectively skip your period. This method is done either in an extended use pattern for two to three months or in a continuous use pattern for an entire year. The most common side effect of using birth control pills in this way is breakthrough bleeding in the first several months. You may even notice that the blood you see is dark brown, which may mean that it’s old blood.

With IUDs, you may experience changes in your menstrual flow until your body adjusts to influx of new hormones. With the copper IUD, there are no new hormones, but you could still experience changes in your menstrual flow. Bleeding between periods is also a common side effect for both kinds of IUDs. It’s important to tell your doctor if your bleeding is particularly heavy or if you notice spotting or bleeding after sex.

While breakthrough bleeding may be normal and go away on its own over time, you should call your doctor if you’re also experiencing:

  • abdominal pain
  • chest pain
  • heavy bleeding
  • eyesight or vision changes
  • severe leg pain

Sometimes sexually transmitted infections (STIs) — like chlamydia and gonorrhea — can cause breakthrough bleeding. STIs are infections that are passed from one partner to another through unprotected sex.

Breakthrough bleeding can also result from other inflammatory conditions, such as:

Along with breakthrough bleeding, you may experience:

  • pelvic pain or burning
  • cloudy urine
  • abnormal vaginal discharge
  • foul odor

Many infections can be treated with antibiotics, so see your doctor if you’re experiencing symptoms. If left untreated, infections can lead to infertility and other serious health issues.

Any bleeding when you aren’t expecting it may concern you, especially if it happens during pregnancy. Sometimes, though, you may experience spotting or bleeding between cycles or during pregnancy if your cervix gets irritated or injured. Your cervix is located at the base of your uterus, so any bleeding from a sensitive cervix due to irritation or injury would cause a bloody discharge.

During pregnancy, the cervix becomes soft and may bleed after a vaginal exam or after having sex. It may also bleed if you have what is called cervical insufficiency, a condition in which the cervix opens too early before your due date.

Bleeding or spotting during pregnancy may or may not signal a problem. One condition that may cause bleeding during pregnancy is called a subchorionic hematoma or hemorrhage.

In this condition, the chorionic membranes separate from the sac, between the placenta and uterus. This can cause clots and bleeding. Hematomas may be large or small and, as a result, cause either significant or only very little bleeding.

Although most hematomas aren’t harmful, you should see your doctor for diagnosis. They’ll perform an ultrasound to see how large the hematoma is and advise you on next steps.

Most women who experience bleeding during pregnancy deliver healthy babies. Still, bleeding during pregnancy can sometimes be a sign of miscarriage or ectopic pregnancy.

A miscarriage occurs when a fetus dies in the womb before 20 weeks. An ectopic pregnancy occurs when implantations occurs in the fallopian tube instead of the uterus.

Contact your doctor if you experience any other signs of miscarriage:

  • heavy bleeding
  • dizziness
  • pain or cramping in your abdomen, especially if it’s severe

If you’re experiencing a miscarriage, you may bleed for two weeks or longer. If your uterus doesn’t empty completely, your doctor may suggest having a dilation and curettage (D&C) or other medical procedure to remove the remaining tissue. Ectopic pregnancy usually requires surgery.

If fibroids develop in your uterus, it can lead to breakthrough bleeding. These growths may be caused by anything from genetics to hormones. For example, if your mother or sister has fibroids, you may be at a higher risk of developing them yourself. Black women also tend to have a higher risk of developing fibroids.

Along with breakthrough bleeding, you may experience:

  • heavy bleeding during your menstrual period
  • periods lasting more than one week
  • pain or pressure in your pelvis
  • frequent urination
  • trouble emptying your bladder
  • constipation
  • backache or pain in your legs

If you’re experiencing any of these symptoms, see your doctor.

It’s difficult to tell if the bleeding you’re experiencing between cycles is breakthrough bleeding or implantation bleeding. Implantation bleeding is any bleeding or spotting you experience 10 to 14 days after conception. Some women experience this, and others may not.

Both may happen between normal menstrual cycles. Both may be light enough to not require a tampon or pad. That said, breakthrough bleeding can occur at any time, and implantation bleeding only happens a few days before a missed period.

The best way to tell if you’re experiencing implantation bleeding is to either take a home pregnancy test or visit your doctor for a blood test.

You may or may not be able to prevent bleeding between periods. It all depends on what’s causing your bleeding.

Whether or not you should wear a tampon or pad depends on the reason for your bleeding. For example, if you believe your bleeding is a result of hormonal birth control, it’s likely fine to wear a tampon. If your bleeding may be the result of an impending miscarriage, it’s better to use pads.

It’s best to consult with your doctor for guidance on how to manage your bleeding. If it’s happening frequently, you should make an appointment with your doctor. Your doctor can help identify the cause of the bleeding and treat your symptoms.

Breakthrough bleeding isn’t necessarily a reason for concern. For example, you may experience bleeding outside of your normal menstrual period due to the birth control you’re taking or irritation to your cervix. In these cases, the bleeding will likely go away on its own without treatment.

If you suspect you have an STI, fibroids, or other medical issue, take note of any other symptoms you’re experiencing and call your doctor. In general, you should see your doctor if the bleeding is heavy or accompanied by pain or other severe symptoms.

Women who have reached menopause should also pay close attention. If you haven’t had a period in 12 months and start noticing abnormal bleeding, it’s important to tell your doctor. Bleeding after menopause may be a symptom of anything from infection to hypothyroidism.