its a quick jab in the thigh normally adminsitered as soon as they deliver the baby that is a synthetic form of Oxytocin ( which your body creates after delivery of your baby and can be helped by BF your baby ) it causes the placenta to detatch and contracts the uterus, having the Injection supposedly reduces blood loss post birth but from my recent research it actually probably doesnt it just traps the blood flow and clots in the uterus so that a few hours later when the woman goes to the bathroom to pee and shower they loose the blood and clots then, i know with ds1 i bled really heavily 4-12 hours after he was born then it stayed quite heavy for 5 wks dropping down only at week 6 before stopping, with ds2 i bled a tiny bit more post birth but not enough to be consider a hemmorage and the bleeding in the following weeks was alot less, i believe it was down to having a physiological 3rd stage with ds2 rather than the managed 3rd stage i had with ds1