Rachel MacPherson is a health writer, certified personal trainer, and exercise nutrition coach based in Montreal.

Monique Rainford, MD, is board-certified in obstetrics-gynecology, and currently serves as an Assistant Clinical Professor at Yale Medicine. She is the former chief of obstetrics-gynecology at Yale Health.

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.

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:

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.

Two major symptoms of a miscarriage are:

If you experience pain or cramping with or without bleeding and you think you might be pregnant, seek emergency care.

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

Symptoms of an ectopic pregnancy include:

Call for emergency care if you suspect an ectopic pregnancy or experience pain.

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.

Cervical ectropion is a normal physical anomaly that people are born with. Hormonal changes can cause it, making it more likely during adolescence, pregnancy, or when taking an estrogen-containing contraceptive like the pill.

Several other causes of bleeding not due to pregnancy include:

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.

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.

If you are pregnant, your body will increase human chorionic gonadotropin (hCG) production, which a test can detect.

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

Some signs of implantation bleeding are:

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.

Visit your healthcare provider about irregular or unexpected vaginal bleeding. 

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. 

Implantation—when a fertilized egg attaches itself to the uterine lining—typically occurs six to 12 days after conception. 

In a typical 28-day cycle, implantation bleeding can occur between days 20 and 24. Implantation bleeding is typically light pink to rust-colored discharge, spotting, or light bleeding. It is often accompanied by light cramping and possibly headache, nausea, lower backache, mood changes, and breast tenderness. 

Period blood tends to be heavier, darker in color, and last longer than implantation bleeding.

Implantation bleeding can last for a few hours or a day or two. It is commonly very light and can be constant or start and stop on and off for a few days.

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Committee opinion no 700: methods for estimating the due date. Obstetrics & Gynecology. 2017;129(5):e150-e154. doi:10.1097/aog.0000000000002046

Matiluko AF. Cervical ectropion. Part 1: appraisal of a common clinical finding. Trends in Urology Gynaecology & Sexual Health. 2009;14(3):10-12.

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