During your pregnancy, your body prepares itself for a certain predictable amount of blood loss that will be experienced during the delivery. The average woman loses a pint of blood during the delivery, or two cups of blood. The body readies itself for this event by doubling its blood volume. Postpartum hemorrhage, however, is the term that signifies a mother has lost more than 2 cups of blood (500 cc) during a vaginal birth or more than 1,000 cc in the case of a cesarean delivery.
While modern obstetric medicine is quite advanced and has some truly amazing technology, excessive postpartum blood loss still remains a major cause of maternal death after delivery. By the time a woman reaches her 40th week of gestation, 700-1,000 cc's of blood flow to her uterus each minute. Because of this strong blood flow to the pelvic region, blood loss can be very fast until medical intervention is at last successful in stanching this flow of blood.
After the birth, and after the placenta has been expelled it is usual for the uterus to contract. The contraction of the uterus shrinks and compresses the blood vessels so that the bleeding slows and for the most part, stops.
Sometimes though, the uterus fails to contract so that there is nothing to check the bleeding. This is known as uterine atony. This can happen when the uterine muscle is exhausted at the end of a lengthy or very fast labor. Atony may also occur after an induced labor. Other causes of uterine atony include an incomplete delivery of the placenta and uterine clots. Sometimes, the birth of a large baby or a twin birth can over-enlarge the uterus and weaken its ability to contract.
Uterine atony is not the only cause of postpartum hemorrhaging. This type of excessive blood loss can also occur in response to lacerations of the vagina or cervix, or after an episiotomy.
After delivery has occurred, there will be signs that the separation of the placenta has been accomplished. These signs include a gush of blood and the lengthening of a cord. Two hormones are then released by the body: prostaglandin and oxytocin. These hormones encourage muscle contractions and signal the uterus to begin contracting. These contractions then limit the blood loss. Most of the time, the placenta comes out after a few maternal pushes, though sometimes the midwife may give the cord a gentle tug during a uterine contraction.
If your physician feels you may be vulnerable for postpartum hemorrhage, there are certain precautions he can take during the time of your labor and delivery. You will be given intravenous fluid and be administered a dose of oxytocin either during or right after the delivery. In addition to these measures, you will be given an external massage over the area of your uterus and some gentle traction will be applied to the cord after your baby is born.