Hi N.,
I had spotting at 3 different times when I was pregnant with my daughter. The first time was just before I got my positive pregnancy test and I believe that was implantation spotting. Then I had spotting again just before the 6wk mark and again around 9 weeks. Each time it was just a little bit and only lasted a couple days. My doctor did the HCG test and my numbers were rising as they should. They also did an ultrasound and the baby looked fine. My daughter was born and is now the most healthy 4 year old you have ever seen.
Then I got pregnant again last December. I began spotting a couple days before I was supposed to start my period. This time the spotting lasted almost 2 weeks and did not get lighter over time. I went in again for my HCG tests and my numbers were going down not up. Unfortunately, I did end up miscarrying.
I am now 29 weeks pregnant with our second child. I did have some light spotting right before I would have started my period again. This time I went to to the OB's office right away and they checked my HCG (numbers were great and going up). They also checked my progesterone levels. It turns out they were a bit low and that may have caused some of the spotting. I was prescribed progesterone suppositories to take throughout the first trimiester until the placenta takes over production of progesterone. I have not had any more spotting with this pregnancy and so far baby is looking great.
I will also say that I automatically thought that spotting equals miscarriage. But since it happened to me, I have talked to other people. And I have honestly found more women who have had some minor spotting at one point or another during pregnancy than women who have never experienced it! I think it is definitely something that needs to be checked out by your doc, but that it can be completely normal during pregnancy.
Sorry this has been a book but I hope some of it was helpful/reassuring to you. Good luck with your pregnancy!