Implantation bleeding is light bleeding that sometimes occurs when a fertilized egg implants itself in your uterine lining. This usually happens about 6 to 12 days after fertilization.

During implantation, blood vessels in your uterine lining can burst, releasing blood.

It can be easy to mistake it for the start of your period, but implantation bleeding is sometimes accompanied by other symptoms, such as:

  • backaches, especially in the lower back
  • breast tenderness
  • headaches
  • mild cramping
  • mild nausea

Implantation bleeding is usually pretty light and only lasts for a day or two. It might be enough to warrant a wearing a pantyliner, but it’s usually not enough to soak a tampon or bad.

Still, implantation can be on the heavier side in rare cases. This usually only happens in those who have an underlying bleeding disorder that affects their blood’s ability to clot.

Implantation bleeding is typically lighter in color than menstrual blood, which is usually dark red.

Generally, implantation bleeding can range in color from a light pink to a rust-like color.

Implantation bleeding doesn’t usually result in clots. Clotting is typically the result of heavier menstrual flow or bleeding.

Bleeding outside of your usual menstrual cycle isn’t always implantation bleeding. This is especially true if the bleeding is heavy.

Other potential causes of unusual heavy bleeding include:

  • Bleeding disorders. Hemophilia, von Willebrand disease, or other disorders can cause uncontrolled or excessive bleeding.
  • Cervical infection. These can be due to a sexually transmitted infection, such as chlamydia or gonorrhea.
  • Ectopic pregnancy. This condition occurs when the fertilized egg implants itself outside the uterus, often in the fallopian tube. This is a medical emergency requiring immediate treatment.
  • Birth control. An infection from an intrauterine device (IUD) or hormone changes due to birth control pills can cause bleeding.
  • Uterine cancer. A rare cause of uterine bleeding, it’s possible that uterine cancer can cause symptoms similar to implantation bleeding.
  • Uterine fibroids. These noncancerous uterine growths can cause bleeding.
  • Uterine polyps. Uterine cell overgrowth can lead to uterine polyps, which may bleed due to hormonal changes.

It’s best to follow up with your healthcare provider about any unusual uterine bleeding, especially if it’s on the heavier side or is accompanied by clots.

If you’re already pregnant and experiencing what seems like implantation bleeding, you may just be experiencing a fairly common symptom in early pregnancy.

According to the American College of Obstetricians and Gynecologists, an estimated 15 to 25 percent of women experience bleeding in the first trimester. This can be because the cervix develops additional blood vessels to support a woman’s growing uterus during pregnancy.

Still, the only way to be sure about the underlying cause of your bleeding is to see your healthcare provider. Depending on your other symptoms and medical history, they’ll likely start with some blood tests and an ultrasound.

Implantation bleeding can be one of the earliest signs of pregnancy. However, implantation bleeding isn’t usually heavy unless you have an underlying bleeding disorder.

If you experience heavy bleeding outside of your menstrual cycle, make an appointment with your healthcare provider. They can help find the cause and provide treatment options.