If you are seeing spots or streaks of brownish blood don't worry. Brown blood is old blood and often the issue is past by the time you notice the blood.
Bright red blood spotting or streaking can be worrying but most of the time is not a cause for concern if it is not accompanied by cramping, soreness/pains, fever or chills.
Heavy bleeding is a cause for concern and could indicate an ectopic
pregnancy.
Miscarriages, stillbirths, infections, cervix irritation/inflammation, pieces of the mucus plug etc are all possible causes for bleeding or spotting in pregnancy as well as placenta previa or placenta abruption.
Other Resources

