Miscarriage is the loss of a pregnancy at any time up to the 24th week.

http://www.patient.co.uk/health/miscarriage-and-bleeding-in-early-pregnancy

The most common cause of bleeding is miscarriage. Miscarriage is the loss of a pregnancy at any time up to the 24th week. A loss after this time is called a stillbirth. At least 8 miscarriages out of 10 actually occur before 13 weeks of pregnancy.