What Is Implantation Bleeding?

Implantation bleeding occurs when a fertilized egg attaches itself to the uterine lining (endometrium). Implantation is typically six to 12 days after fertilization and can cause some spotting or light bleeding, although this is not always the case.

Approximately 15% to 25% of those who become pregnant will experience bleeding in the first trimester. Implantation bleeding is a normal symptom that doesn’t require any medical attention. However, there are important signs to watch for in case of something more serious.

Types

There are various reasons why you might see bleeding, including the beginning of your period. You may even assume implantation bleeding is the start of your period since the timing of both are similar.

Many of the signs of implantation are similar to your menstrual cycle, so it might be difficult to know if you are pregnant unless you have missed a period.

The three types of bleeding related to your cycle and/or pregnancy are:

• Implantation bleeding: When a fertilized egg attaches itself to the uterine lining (endometrium).
• Ovulation bleeding: Light bleeding or spotting that occurs when an egg is released from the ovary.
• Period bleeding: If a fertilized egg does not implant in the wall of your uterus after ovulation, the lining sheds.

Early miscarriage can also cause bleeding and occurs in about 10% of known pregnancies.

Unlike the other causes of bleeding, early miscarriage typically causes heavier, darker blood flow and cramping, with visible tissue and blood clots passing through the vagina.

The pain and bleeding of miscarriage can be greater than during your period. Early miscarriage can occur five weeks after ovulation.

Bleeding can also occur during an ectopic pregnancy—when a fertilized ovum implants outside of the uterus.

Cervical erosion, also called cervical ectropion, can also cause light bleeding or spotting. The cervix has an increased blood supply during pregnancy and can sometimes bleed, which is typically harmless.

This bleeding can happen as a result of the cervix being irritated during a pelvic exam. Sometimes this happens after sexual intercourse, which you should speak to your healthcare provider about.

Cervical ectropion can also happen when you are not pregnant. It is a condition in which the cervical canal turns outward, exposing the cervix’s inner cells to the vaginal canal’s acidic environment, causing it to become red, raw, and potentially bleed.

Several other causes of bleeding not due to pregnancy include:

• Fertility treatments such as IUI or IVF procedures
• Sexual intercourse
• Endometriosis
• Beginning, ending, or missing doses of hormonal contraception
• Fertility drug side effects
• Diseases of the thyroid
• Polycystic ovary syndrome (PCOS)
• Fibroids or polyps
• Infections
• Ovulation
• Menstruation
• Cervical ectropion

Purpose

When an egg is released from an ovary, usually once per month, ovulation occurs. At this point, the egg travels through the fallopian tube.

If an egg is penetrated by a sperm and becomes fertilized due to intercourse, it starts to divide into multiple cells while moving through the fallopian tube to the uterus.

A fertilized egg takes several days to travel down the fallopian tube before either implanting or being shed by the body if implantation fails. If it does implant, human chorionic gonadotropin (hCG) hormone is produced in the uterus, preventing the uterine lining from being shed.

If implantation does not occur, the egg and uterine lining are shed during the menstrual period.

After dividing into about 100 cells, the egg becomes what is known as a blastocyst. The uterine lining has many blood vessels, so when the fertilized egg (blastocyst) pushes into the lining, bleeding can occur. This blood will exit through your cervix, just like menstrual flow.

Signs

Implantation bleeding is one of the earliest signs of pregnancy and occurs around the same time you would be expecting your period. Since these two causes of bleeding can be confused, the best way to know for sure if you are pregnant is by taking a pregnancy test.

It’s important to note that many people may not experience any bleeding at all in early pregnancy.

However, there are differences between menstrual blood flow and implantation bleeding. 

Some signs of implantation bleeding are:

• Light pink to rust-colored spotting, light bleeding, or pink-colored discharge
• May come and go, or remain constant
• Can last hours or a few days
• Light cramping
• Headache
• Nausea
• Lower backache
• Mood change
• Breast tenderness

Complications

Implantation bleeding is normal and not a risk factor. If bleeding occurs more than a few days after you expected to get your period, it will not likely be implantation bleeding.

If the bleeding is heavy, constant, or lasts for several days, it is almost certainly not from implantation and should immediately be checked by a healthcare provider.

A Word From Verywell

Bleeding when suspecting a pregnancy can be alarming, but implantation bleeding is a common and normal early pregnancy sign.

It may be difficult to tell if the bleeding you experience is from implantation, your period, or another cause. Be sure to tell your healthcare provider about any bleeding you experience if you believe you may be pregnant, and seek emergency care if you experience abnormal heavy bleeding or pain if you know you are pregnant.