What Is Postpartum Hemorrhage?

Vaginal bleeding is normal after birth. It is mainly caused by the placenta, which delivers food and oxygen to the developing baby while it is in the uterus (womb), detaching from the wall of the uterus. Although bleeding can initially be fairly heavy, it reduces in the days after birth and usually stops within a few weeks.

PPH is different. It can start suddenly and large amounts of blood can be lost very quickly. PPH can be classed as either primary (when 500 mL of blood or more is lost in the first 24 hours after birth) or secondary (when bleeding is heavy or abnormal after the first 24 hours and up to the end of the 12th week after birth). PPH can occur after birth by vaginal delivery or delivery by cesarean section. The contractions that help the placenta to pass out of the uterus after birth also compress the blood vessels in the wall of the uterus where the placenta has been attached. PPH can develop if these contractions aren’t strong enough (this is known as “uterine atony”), if part of the placenta stays attached to the wall of the uterus, or if any internal cuts or tears happen during birth.

How Serious Is Postpartum Hemorrhage?

PPH is serious and potentially fatal because sudden heavy blood loss can cause a sharp drop in bloop pressure, which can reduce blood flow to other organs, including the brain and heart. It is treated as a medical emergency. It is important that new mothers keep their healthcare team and partner aware of any changes in their bleeding, and act quickly if bleeding suddenly becomes very heavy. Other symptoms that should be reported include blurred vision, dizziness, feeling faint, worsening pelvic or abdominal pain, nausea or vomiting, an increased heart rate and/or breathing rate, and pale or clammy skin. These symptoms may only start after the woman has left the hospital. Although PPH is estimated to occur in 1–10% of pregnancies and remains a key cause of maternal death (mortality) worldwide, the earlier the bleeding is treated the more successful the outcome.

What Increases Your Risk of Postpartum Hemorrhage?

If a woman is considered to be at high risk of PHH she will be advised to give birth in a hospital setting. Before birth, placental problems (like the placenta being located relatively low in the uterus or starting to detach from the wall of the uterus before it should) can increase a woman’s risk of PPH. Other risk factors include an overstretch uterus, which can be caused by having had more than one previous pregnancy, too much amniotic fluid (the fluid that surrounds the baby while it is in the uterus), and having a multiple pregnancy (expecting two or more babies at the same time).

During the birth, risk factors include a delay in the placenta being delivered or some of it remaining attached to the wall of the uterus, having a large baby, and the baby being delivered by forceps or ventouse. Another known risk factor is if the woman has a blood clotting disorder or other blood-related condition. The blood clotting system (known as the “coagulation” system) is activated when the lining of a blood vessel is damaged and regulates the process by which liquid blood changes to a gel, forming a blood clot, which stops the bleeding and starts the repair process.

How Does the Blood Clotting System Work?

The process by which blood clots are formed involves a number of proteins and platelets (a type of blood cell). When a blood vessel is damaged, such as when the placenta detaches from the uterus, platelets cluster at the site of damage and bind together to seal it. The platelets have receptors on their surfaces that bind a molecule called thrombin, which converts a soluble protein called fibrinogen into a different form called fibrin. Fibrin can form long, tough, insoluble strands that bind to the platelets and cross-link together to form a mesh on top of the platelet plug. Lots of different molecules are involved in this process, but platelets and fibrin are major players.

How Does Blood Clotting Relate to Postpartum Hemorrhage?

Some researchers have suggested that if a woman has a lower than normal level of platelets in her blood (a condition called “thrombocytopenia”) before she gives birth she may be at increased risk of PPH. Thrombocytopenia is estimated to occur in around 10% of pregnancies. There is also some evidence that the levels of a blood protein called coagulation factor XIII affect PPH risk. Coagulation factor XIII stabilizes fibrin as blood clots form. If low levels are present in the blood, clots can be less stable and the risk of bleeding increases.

What Did the Study Investigate?

The authors of the study evaluated whether a woman’s platelet count (the number of platelets measured in a sample of blood) measured before birth is linked to the extent of blood loss after birth. They also looked at whether there is an association between platelet count and levels of coagulation factor XIII, either before or after birth. They did this by looking at data collected as part of a previous study (this is termed “secondary analysis”) that analyzed the impact of coagulation factor levels before birth on blood loss after birth for 1,300 women. They found that the higher a woman’s pre-birth platelet count, the lower the probability of them developing PPH, and that this was seen for women whose babies were delivered either vaginally or by cesarean section. An increase in pre-birth platelet count by 50 G/L was shown to decrease the likelihood of PPH by 16%.

The authors also found that platelet count is significantly correlated (strongly linked) with coagulation factor XIII activity both before and after birth, which suggests that platelets may play an important role in the firmness of blood clots. Coagulation factor XIII is found in the cytoplasm of platelets (the fluid-like area inside a cell that does not include the nucleus, where the genetic information is stored). This suggests that the chance of developing PPH may be influenced not only by the number of platelets in the blood, but also by the availability of coagulation factor XIII in the areas of platelets that are involved in its blood clotting role.

The authors state that these findings support the importance of measuring platelet counts when identifying women who may be at high risk of PPH. Recent medical guidelines in Germany, Switzerland, and Austria have included platelet transfusion to increase the number of blood platelets in a six-step approach to treat continued bleeding. It is possible that platelet therapy may become useful in the prevention and treatment of PPH in the future.

Note: The authors of this paper make a declaration about patent ownership as well contributions to a new guideline. It is normal for authors to declare this in case it might be perceived as a conflict of interest. For more detail, see the Conflict of Interest Statement at the end of the paper.