Immediately after your delivery and expulsion of the placenta the muscles in your uterus will contract strongly.In some cases, the uterine muscles are stretched too much and they can not contract enough. As a result, the veins are not pinched enough and you lose more blood than the 800 milliliters considered to be normal and harmless.
Too much stretched uterine muscles can be the result of a very big baby, a multiple pregnancy, a very long birth or if you have had previous children. In about 1 in 20 births more blood is lost than normal.
In 75% of the cases, too much blood loss occurs due to improper contractions of the uterine muscles. Other causes include failure of placenta, clotting disorders, ruptured cervix or vagina.
If you lose more than one liter of blood, the doctor will immediately massage your uterus and give you a medication that will allow the uterus to contract. If you have lost a lot of blood you can also get an infusion to replenish blood and moisture. The medicines work within minutes. Depending on the medicines used, you may suffer from headaches, nausea and cold chills.
If medicines do not work then the doctor will try to close the bleeding. This can happen both chirurgically and non-surgical.
Removing the uterus is the last "solution", if nothing else seems to stop the blood loss. If you want more children, every effort will be made to prevent this. Medical techniques are continuously improved.
From angelababy In Q&A