Implantation bleeding is usually defined as a very small amount of bleeding or spotting that occurs when the embryo implants into the lining of the uterus. It occurs shortly before the time you would expect to have a menstrual period, and it can confuse you into believing that you have a period. However, it tends to be much lighter than menstrual bleeding. 

Implantation is the attachment of the fertilized egg (now called a blastocyst) has completed its travel through the fallopian tube and adheres to the lining of the uterus. Implantation happens about a week after ovulation with a range of 6-12 days after fertilization.

At the time of ovulation, the egg is released from the ovary. Fertilization of the egg by a sperm usually happens within 12-24 hours after ovulation in the distal part of the fallopian tube. The egg/sperm combination is now called a "zygote" and begins traveling down the Fallopian tube towards the uterus. During that time the fertilized egg multiplies into the first 2, then 4, and then 8 and more cells. The fertilized eggs which by then is known as the blastocyst enter the uterine cavity about 5-6 days after fertilization and adheres to the lining of the uterus within 1-2 days (6-9 days average after ovulation/fertilization) after reaching the uterus.  

Are there implantation symptoms?

The blastocyst is a cluster of tiny cells, smaller than the head of a pin. Most women have no symptoms on that day. Some women report some spotting or bleeding around the time of implantation. Most women report this bleeding to be brown in color though some mention it to be more reddish. Most women report at most a few drops of blood — may be one to two small red or brown spots in the underwear — though others report a more substantial amount, rarely if ever does it approach the appearance of menstrual bleeding. If your bleeding is similar to a menstrual cycle, chances are that it's not implantation bleeding.

It's likely that most women who become pregnant do not experience implantation bleeding, and many women experience some spotting but they are not pregnant.

If you experience bleeding regularly after ovulation and you are not pregnant then you may want to discuss with your doctor whether some tests can be done to make sure everything is OK.

When does implantation bleeding or spotting happen?

Implantation bleeding and spotting happen at implantation, about 6-12 days after ovulation and fertilization. Implantation is the attachment of the fertilized egg, the blastocyst into the lining of the uterus. Implantation happens about a week after ovulation with a range of 6-12 days. Some women report some spotting or bleeding around the time of implantation. 

The bleeding/spotting as a result of implantation usually occurs about a week before your period is due to begin (or 9 days after ovulation). Some women refer to this as spotting while others do not even notice the bleeding at all. The closer to the day when your cycle is supposed to begin that the bleeding is noticed, the less chance there is of it being implantation bleeding.

Keep in mind that the blood associated with implantation bleeding is usually not fresh so it may not look like regular menstrual bleeding. The time it takes for these drops to move out of the body ages the blood and it will usually appear dark brown, or even black by the time the spotting occurs. Occasionally the blood associated with implantation bleeding may be fresh and appear redder.

Is implantation bleeding a first pregnancy sign?

Implantation bleeding and spotting are among the very first of the typical pregnancy symptoms and pregnancy signs. It is thought to happen when the fertilized egg attaches to the lining of the uterus. Some women experience bleeding upon implantation while others never do. Having bleeding can also be confused with having menstrual bleeding or your period. This form of bleeding when you are pregnant is normal and requires no specific treatment but you can have a normal pregnancy without it.

What is the difference between implantation bleeding and your period?

There are four characteristics of bleeding or spotting that can differentiate between a period or implantation symptoms. You can identify whether the bleeding is associated with implantation or a menstrual period by the following characteristics:

1. Timing: Implantation bleeding happens about 6-12 days after ovulation while a menstrual period happens 14 days after ovulation
2. Character: Implantation bleeding is just a couple of drops while a menstrual period is much more
3. Color: A menstrual period is usually bright red while implantation is more brownish
4. Duration: Bleeding associated with implantation lasts up to one day while a menstrual period lasts 3-5 days 

Is implantation bleeding common?

Most women who do become pregnant do not experience implantation bleeding, and many women experience some spotting but they are not pregnant. Implantation bleeding is fairly common with pregnancy and approximately twenty to thirty percent of women will have spotting at implantation.

If you experience bleeding regularly after ovulation and you are not pregnant then you may want to discuss with your doctor whether some tests can be done to make sure everything is OK.

If you have some light spotting before your period would normally start this is not something to worry about but it may be a sign of pregnancy.

Are there any other reasons for bleeding or spotting early in pregnancy?

Other than implantation, there are many other reasons for women to bleed or spot early in pregnancy. Implantation bleeding is not typical after you already have a positive pregnancy test. In early pregnancy (first 6-8 weeks of the pregnancy) other causes of spotting or bleeding include:

• Threatened miscarriage: Up to 50% of pregnancies end in a miscarriage, the loss of the pregnancy. Bleeding could be among the first signs of a miscarriage, especially if it's associated with cramping.
• Sexual intercourse: Bleeding or spotting can happen after sexual intercourse.
• Ectopic pregnancy: An ectopic pregnancy is when the embryo implants outside the uterus, and it's usually accompanied by pain and cramps on one side but also on both sides. An ectopic pregnancy is life-threatening and requires you to see a doctor right away.