There is a slight increase chance of haemorrhaging if you do not have the injection. (I’m not sure what the numbers are). However the worst haemorrhage I have seen was after the woman had the injection. Breastfeeding very soon after birth helps to prevent excessive bleeding, as can massaging your fundus. (The top of the uterus). Also if you do start to haemorrhage they can give you the injection then, and if this injection is given into a vein then the drug will take effect within a minute.