What can someone do to tell the difference between a period and a 1st-trimester miscarriage?

Difficult to tell. It's often difficult to distinguish a normal period from a miscarriage just by your bleeding. First, a pregnancy test should be performed. However, a positive pregnancy test doesn't necessarily mean miscarriage is the setting of bleeding. To tell for sure, you should be evaluated by an obgyn. He or she can perform an ultrasound and trend your beta HCG and determine what's going on.
Pregnancy test . It is often hard. The only way to know is to check a pregnancy test. If you have a positive pregnancy test and are bleeding it is a good idea to follow up with your gyn.