Well... not knowing the exact answer to your question, I googled it.. this is what I found...
It can happen at the time the fertilized egg implants in the uterus, on average between 6 to 12 days past ovulation. you will usually experience implantation a week or more before you would expect your period, depending on when you ovulate. Does your OB not have an emergency on call Dr you can call? If not, I would go ahead and go to the ER. Just to be safe. I had preterm labor with my daughter and had I not gone to the ER when my dr said it was braxton hicks she would have been born at 22 weeks and may not have made it. Instead, she was 2 weeks late!! I'll be praying for you, let us know how things go!

Also visit this site... http://www.midwiferytoday.com/forums/topic.asp?TOPIC_ID=6772

Me again... just worrying for you... From what I have read, as long as it isnt heavy bleeding and ONLY brown in color, no pink... then it could be some left over implantation bleeding, but you should still visit your doc asap either way. If it is brown and red or pink, then that is cause for more concern.

Thanks, the hospital suggested getting off my feet, getting some sleep, and if cramping wakes me up to come in immedatly. So i am off to bed. Thanks for all you help!

I had some spotting at 7 weeks too. It was very light, kind of like the very end of a period. The dr ordered an ultrasound and some blood work, and wasn't too concerned considering there wasn't any cramping and it wasn't a red or pink color. I asked her if there was anything I could do to prevent a miscarriage if that's what was happening and she said no, I should just do what I would normally do. She said if I had several severe cramps that I should go in or if my bleeding became heavy or bright red. I rested a little anyway and just tried to relax, knowing that there wasn't anything I could do to stop anything bad from happening, and if it was a miscarriage, it was for a good reason. Turned out taht everything was normal.

Some women get their periods while pregnant, and the baby is just fine. I also read that sometimes the progesterone level isn't high enough to keep your body from shedding a small amount of uterine lining, like if you were having your period. It doesn't harm anything.

There are many harmless reasons for a little spotting during pregnancy, so just do your best to relax as long as you're not having pain with it.
Chances are

I spotted though out my first 4 months and twice has a major bleed and had to go to the hospital. I am now 7 and a half months and everything is fine. Just watch it and if you are concerned at all, I suggest seeing your Dr. or going to the ER to put your mind at ease. You need to be stress free!

I had spotting at that time too with this pregnancy (I am now 13 weeks) and my last pregnancy. It was light and brown only. It turned out with both of them it was a cyst that pregnant women get to produce more hormones to keep the pregnancy going. Harmless but scary I know.

I've been pregnant 5 times and bled in 3 of the pregnancies. Only once did it lead to miscarriage. Hang in there - many women bleed during pregnancy with no other complications. You should be able to get and ultrasound now to check the baby.

If your 7 weeks implantaion is done, but if your spotting is brown and just spotting I wouldn't worry....easier said than done. This can be normal in early pregnancy...although still scarey. Did you call the ER or your RE? I would definitly call your OB or RE.
The best thing you can do is stay calm.
Keep us posted

I had bleeding with all 3 of my pregnancies, as a matter of fact with my first 2 I had 3 days of it, and it was more brown then anything but it also looked like it could have been a light period to, and I have had horrid cramps right around 6/7 weeks or so(usually right after I found out I was pregnant) I have always been told it's normal and obviously it is and happens alot judging by the replies. Call your ob though and maybe you can get in to see him/her just to ease your mind a little,and make sure everything is ok.

I understand your concern -- so many thoughts can haunt you when you don't know why you're spotting. I had light implantation bleeding about two weeks before my missed period. Then, I bled and spotted from seven weeks until thirteen weeks. I bled and spotted the colors my doctor & articles on the internet said were dangerous. Each time I went in to my doctor, I had a sonogram. My husband & I were happy to see the baby & hear the heartbeat each time. If you can get a positive sonogram, you may feel a lot better. I'm now only 15 weeks and haven't bled in two weeks. Hang in there. The more I ask around, the more women I find who had full blown periods up until their 4th or 5th month and still gave birth to healthy babies. Keep us informed -- all the best to you...

I would call your Dr. and ask them because it can be implantation bleeding. I don't want to scare you but it could also be a sign of a miscarriage. My miscarriage started like that in August.. But remember that if you are having a miscarriage that God had other plans for your child and that he is taking care of them up in Heaven with him.. A miscarriage happens when there is something wrong with the baby. The Dr. told me that is means that the genetics weren't there.. But definitely call your Dr. as soon as you can.. I will be praying for you..