As with the length of a period, the amount of blood lost during one cycle was highly variable. Light cycles were ones in which women bled fewer than 36.5 milliliters (ml). The medium tertile was for cycles between 36.5 and 72.5 ml of blood loss, and the heavy tertile was for cycles where there was more than 72.5 ml of blood lost. For the one-third of cycles defined as light, the average amount of blood lost was 15.2 ml.
