What is considered a "heavy" period in an adolescent girl?

A typical period should not lead to iron deficiency anemia as your body should be able to recover the blood loss during your period and this should not lead to reduction in your iron stores. If your period lasts 7 or more days, or you have to change your pad more than every 1-2 hours, pass clots larger than a "grape" size, or are unable to change your pad fast enough and it causes "flooding" or overflow onto your clothes, then you should contact your doctor and alert them.