I had the same happen to me at 6+1 it was called a heamotoma mine was only 1cm and I'm now 13+3 and it had gone
This is caused, in the very early stages of pregnancy, by the egg implanting itself into the wall of the uterus. Because it occurs around the same time as you might have had your period, this makes it hard to distinguish between the two causes.
Hormonal or 'Breakthrough' Bleeding.
You might expect your pregnancy hormones to overwhelm your normal hormonal cycle but this doesn't always happen. Some women report bleeding during early pregnancy that strongly resembles having periods during pregnancy. It is actually now thought to be caused by the variation in background hormonal levels that just happen to be greater in some women than in others.
A Cervical Erosion
This is an area of softer tissue near the neck of the womb and it can sometimes bleed.
A Cervical Polyp
Just like the cerival erosion, a small polyp or benign lump can sometimes be the cause of bleeding or spotting in early pregnancy.
A Cervical Infection
Again, if it causes inflammation of the lining of the cervix, this may cause light bleeding or spotting. You would need to get this checked out and treated by your health professional.
More Serious Possible Causes of Bleeding During Early Pregnancy
The term 'miscarriage' is used to describe the loss of a baby in the first 24 weeks of pregnancy. Sadly, miscarriage is an all-too-common occurrence and it's calculated that about 98% of miscarriages happen in the first 13 weeks of pregnancy. It's possible to lose the fetus before you even realise you're pregnant. In many cases, this may be nature's way of ensuring that only the healthy foetus survives, as we know that in the animal world as well as the human, imperfections are quite common. But it's also known that some women are more liable to miscarriage than others, for some physiological reason. It's in situations like these that immediate rest and professional care the moment you experience any bleeding during early pregnancy may prevent a miscarriage. If you are worried about miscarriage or want to find out more, wherever you are in the world, one of the best websites I know is a UK one and is run by the Miscarriage Association.
This occurs when the placenta begins to come away from the wall of the uterus. It may not always cause bleeding but it almost always causes pain, so whatever stage of your pregnancy you're at, if you experience sharp abdominal pains or severe cramping, call a doctor right away.
There is about a one in a hundred chance that a woman may have an ectopic or tubal pregnancy. This is when a fertilised egg implants itself outside the womb, in one of the fallopian tubes. As the fetus grows the mother experiences pain and bleeding. This is a very serious medical emergency, as if the tube ruptures, the resulting internal bleeding can kill the mother. Please do not, under any circumstances, try to ignore bleeding accompanied by severe pain, or any severe pain even on its own, during early pregnancy. Click here if you need to know more about ectopic pregnancy.
In late pregnancy it can sometimes happen that the placenta is still lying low in the womb instead of having migrated upwards, as it should. In such a case, the baby's route down the birth canal is blocked by the placenta. Any bleeding late in pregnancy must be carefully checked out, using ultrasound and/or a pelvic examination, in order to make sure it's not placenta praevia. If it is, you will probably need to have your baby delivered by caesarian section.
These are the main reasons why you might experience bleeding in early pregnancy - and I have included some references to serious reasons not to ignore it in later pregnancy too, simply because they are so important to know about.