Its a gestational sac. How far along are you? Anytime you bleed during pregnancy
it is classified as a "threatened abortion". during early pregnancy
the sac can detach a little bit from the wall or have a blood clot behing it.This is usually called a subchorionic hematoma. There isn't anything that you can do if you are in early pregnancy
to prevent a miscarriage except to not have sex until you haven't bleed for one week or your doctor gives the ok.