Overview of Postpartum Hemorrhage

Postpartum hemorrhage is a significant loss of blood after giving birth, and it’s the number one reason for maternal morbidity and maternal death around the world. Specifically it’s defined as losing more than 500ml of blood after a vaginal delivery or more than 1000ml after a cesarean section delivery. Of course, deliveries can be messy and it’s impossible to measure the precise amount of blood that’s lost, and there’s the possibility of internal bleeding. So additional criteria to consider for postpartum hemorrhage include a decrease of 10% or more in hematocrit from baseline, as well as changes in the mother’s heart rate, blood pressure, and oxygen saturations —all of which suggest a significant blood loss. Significant bleeding in the first 24 hours after delivery is called primary postpartum hemorrhage, and after that it’s called secondary, or late, postpartum hemorrhage.

The most common causes of postpartum hemorrhage can be lumped into four groups which can easily be remembered as the “4 Ts”: Tone, Trauma, Tissue, and Thrombin. Tone refers to a lack of uterine tone, also known as uterine atony—basically a soft, spongy, boggy uterus, and this is the main cause of postpartum hemorrhage, generally resulting in a slow and steady loss of blood. Now, the uterus is a muscular organ wrapped by three layers of smooth muscle called the myometrium, which contracts during labor to dilate and efface the cervix and ultimately push out the fetus and placenta.

After delivery, the myometrium continues to contract and this squeezes down on the placental arteries at the point where they are attached to the uterine wall, which clamps them shut, and therefore reduces uterine bleeding. The contractions continue for a few weeks after the delivery.

With uterine atony, though, the uterus fails to contract after birth, and those placental arteries don’t clamp down, which leads to excessive bleeding and postpartum hemorrhage.

Uterine atony can be caused by several things, repeated distention of the uterus as a result of multiple pregnancies, overstretching from twins or triplets, or any condition that causes too much uterine stretching can interfere with efficient uterine contractions and lead to diminished tone and eventual uterine atony. Uterine atony can also occur when the uterine muscles fatigue during the delivery process because of a prolonged labor. It can also happen when a woman is unable to empty her bladder, since a full bladder can push against the uterus and interfere with uterine contractions.

Finally, some commonly used obstetric medications like anesthetics (especially halothane), as well as magnesium sulfate, nifedipine, and terbutaline can all interfere with uterine contractions and increase the risk of uterine atony.

Uterine atony can be treated by fundal massage, or massaging the fundus—the upper section of the uterus which is typically near the umbilicus right after birth. Fundal massage causes the smooth muscle in the wall uterine wall to contract and harden. If a full bladder seems to be interfering with contractions, then a woman can urinate or have a catheter placed if she can’t void by herself. Medications to help firm up the uterus can also be given, and if necessary, the bleeding may be stopped surgically.

Alright the next ‘T’, trauma, refers to damage to any of the genital structures—the uterus, cervix, vagina, or perineum. This can include the incision from a cesarean delivery, incidental trauma from a baby coming through the vaginal canal, or trauma from instruments used in delivery. For example, the use of forceps, vacuum extraction, or an episiotomy, a small cut used to enlarge the vaginal opening, which can also cause unintended bleeding. Sometimes the bleeding is in a concealed location and a hematoma can form, which is a mass or collection of blood, and go unnoticed for hours after delivery. A key to recognizing a hematoma is severe pain and persistent bright red vaginal bleeding in spite of a firmly contracted uterus. In general, any trauma-related bleeding is an emergency and the site of bleeding has to be repaired right away—generally by applying pressure and stitching lacerations.

The next T, tissue, refers to placental fragments retained in the uterine cavity. The entire placenta normally separates from the uterine wall in the third stage of labor, but occasionally a part of the placenta can stay behind in the uterus. In placenta accreta, the placenta invades the myometrium so it doesn’t easily separate from the uterus. Placenta accreta or just too much traction on the umbilical cord can both cause the placenta to be retained. This in turn prevents effective uterine contractions, and leads to uterine atony.

The goal with this one is to prevent this from happening in the first place by making sure that the placenta comes out completely intact, and removing any tissue that does get retained as soon as possible.

Thrombin, the final T, refers to the mother having some condition that prevents blood clots from forming normally, for example, a genetic disorder like von Willebrand disease or an obstetric condition like eclampsia and placental abruption which may result in a clotting disorder, and these can lead to disseminated intravascular coagulation or DIC. These are conditions that prevent a clot from forming normally when there’s a bleed, and this can turn even a tiny bleed into a serious problem since it doesn’t stop easily. The treatment for each of these is specific to the specific underlying cause.

Alright so postpartum hemorrhage is an obstetric emergency and maintaining adequate circulating volume is a key priority. Regardless of the cause, intravenous fluids and blood products may be used to ensure that the vital organs are well perfused.

Alright as a quick recap, postpartum hemorrhage is the most common cause of maternal morbidity and mortality around the world, and the causes are the 4 T’s: Tone (atony), Trauma, Tissue, and Thrombin. The most common cause—uterine atony—can usually be managed with fundal massage and medications to help the uterus contract.