For most women, the bleeding that happens after a delivery (whether it is a vaginal delivery or a C-section) lasts no more than 6 weeks on average. Some women only bleed for 4 weeks, and some can bleed for up to 8 weeks. The bleeding that happens after delivery occurs because the lining of the uterus, which has grown to be very thick during pregnancy, sloughs off after delivery and removal of the placenta.
Some women will have bleeding that continues for longer than normal. This can happen for a few reasons. Occasionally, part of the placenta or membranes that make up the amniotic sac (the water sac that the baby lived in for 9 1/2 months), is left behind after removal. Having even a small amount of membranes or placenta still attached to the uterine wall can lead to quite a bit of bleeding.
Another reason for bleeding longer than 6 weeks is choriocarcinoma. This is a very rare condition that can develop after a miscarriage, termination or delivery and involves some of the cells of the placenta, continuing to grow, despite the pregnancy being over. This can be a very dangerous condition, but never gets better on its own. Meaning, the bleeding continues to happen until the patient is treated by her physician.
Lastly, placement of an IUD (intrauterine device) or starting birth control pills after delivery can also be a cause of abnormal bleeding.
Most of these conditions are harmless, but the bottom line is that any bleeding after 6 weeks should be discussed with a health care provider.