I agree with the ladies above, its your mucus plug.
No need to be concerned because its normal but you still need to let your doctor know you lost it.
Ive been having the same thibg. You're losing your mucus plug which is normal.
Could've been your mucus plug. As long as there's no bleeding I wouldn't been too concerned. Then again, no one on here is a doctor so we can't really tell you NOT to be worried. If you're concerned that it wasn't normal, then I would contact your doctor. I'm pretty sure it was your mucus plug though. Don't quote me.
Hope This helps...
Tiff