Blood loss early in pregnancy does not always indicate a miscarriage. For example, there may be an abnormality of the cervix, for example a polyp or inflammation, which causes the cervix to bleed easily. Blood loss mainly occurs after intercourse or after (hard) stools.
A much less common cause of blood loss is an ectopic pregnancy (extrauterine pregnancy, often abbreviated as EUG). The pregnancy is then not implanted in but outside the uterus, usually in the fallopian tube. The risk of an EUG is increased after fallopian tube inflammation or surgery on the fallopian tubes. A pregnancy with an IUD still present or after sterilization can also be ectopic.
In many cases no cause can be found for the blood loss. And the blood loss stops automatically.