The ball of cells, known as the blastocyst, that will form the embryo has now completely embedded within the lining of the uterus and the lining has regenerated over it.
Unfortunately, in the complex process of conception, only about half of all fertilized eggs progress to become a blastocyst and only about half of these go on to become successfully implanted in the uterus.
When the blastocyst embeds, there may be some bleeding, known as "spotting." This often leads to confusion regarding the dating of the pregnancy, not least because it can occur around the time that you would normally start your period.
The color of the blood can vary. In most cases it is pinkish, although bright red blood (fresh blood) can occur, as can brownish, old blood. As long as it is not profuse, the color really doesn't matter. If the bleeding lasts for a short period, and you don't experience discomfort, it's likely that things are just fine, but do see your doctor for a checkup.
Around 25 percent of women will experience some bleeding in early pregnancy, but most go on to full term. However, in some cases, bleeding does mean a miscarriage is occurring so always report the fact that you've bled to your doctor.