After you've been diagnosed with a miscarriage, it's normal to have bleeding -- but how much is too much?
The bleeding associated with a miscarriage can be heavy with large clots without meaning a medical emergency. But if you are soaking through a menstrual pad in under an hour, you should seek medical attention at once. You may be hemorrhaging and might need an emergency D & C to stop the bleeding.
If you are not bleeding that heavily but are concerned that your bleeding seems to be persisting for too long, it's normal that miscarriage bleeding may last for several days. However, the quantity should not remain heavy for more than a few days. If you have had bleeding heavier than an average menstrual period for more than two or three days, it is a good idea to see your doctor to rule out complications.
Hillard, Paula Adams. The 5-Minute Obstetrics and Gynecology Consult. Lippincott Williams & Wilkins, 2008. Page 588.