Relationship between antenatal haematologic biomarkers and postpartum haemorrhage among pregnant women in Nigeria

Every year, millions of women around the world face the dual challenges of carrying a pregnancy and the risk of losing too much blood during childbirth. In many parts of the world, particularly in sub-Saharan Africa, a condition called anemia is a common companion to pregnancy. This happens when the blood lacks enough healthy red cells to carry oxygen, often because the body is running low on iron. When a woman gives birth, the loss of blood is a normal part of the process, but if it becomes excessive, it can turn into a life-threatening emergency known as postpartum hemorrhage. For decades, doctors and researchers have wondered if the state of a woman's blood before she gives birth could predict this danger. The prevailing idea was that if a woman enters labor with low iron or low blood counts, she is more likely to bleed dangerously. However, proving this has been difficult because blood tests taken at the moment of delivery are often influenced by the bleeding itself, making it hard to tell if the low blood count caused the bleeding or if the bleeding caused the low blood count.

To untangle this knot, a team of researchers in Nigeria looked closely at a group of pregnant women to see if blood markers measured weeks before delivery could predict who would face a hemorrhage. They focused on a specific group of women who had already been diagnosed with moderate to severe anemia and were receiving treatment. The study examined whether the levels of hemoglobin, the protein that carries oxygen, and other iron-related markers measured at 36 weeks of pregnancy could forecast the risk of heavy bleeding. The researchers also looked at whether these same markers, when measured again just hours after the baby was born, told a different story. By comparing the blood work from late pregnancy against the actual amount of blood lost during delivery, the team hoped to clarify whether anemia is a cause of dangerous bleeding or simply a sign that bleeding has already occurred.

The study involved 787 women who were part of a larger clinical trial in Nigeria, a country where both anemia and postpartum hemorrhage are significant public health concerns. These women had been receiving treatment for anemia, either through iron pills or intravenous iron infusions, as part of their care. The researchers collected blood samples from these women at 36 weeks of pregnancy, a time when the baby is nearly full-term, and then again within the first hour after delivery. They carefully measured the amount of blood lost during birth using a precise method that weighed the pads used to catch the blood, rather than relying on a visual guess. This allowed them to determine exactly which women experienced a hemorrhage, defined as losing more than 500 milliliters of blood during a vaginal birth or more than 1,000 milliliters during a cesarean section.

When the team analyzed the data, they found a surprising disconnect between the blood levels measured before birth and the risk of hemorrhage. The levels of hemoglobin and iron markers at 36 weeks did not predict who would bleed heavily. Women who had lower blood counts at this stage were not statistically more likely to suffer a hemorrhage than those with higher counts. This suggests that having anemia during the later stages of pregnancy, at least in women who are receiving treatment, does not necessarily mean a woman is at a higher risk of bleeding out during delivery. The researchers noted that because these women were being treated with iron, their bodies were likely responding, and the anemia they had at the start of the study might have improved or changed by the time they gave birth.

However, the picture changed completely when the researchers looked at the blood samples taken immediately after the baby was born. Here, a clear pattern emerged. Women who had lower hemoglobin levels and lower levels of a protein called transferrin right after delivery were significantly more likely to have experienced a hemorrhage. For every small increase in hemoglobin measured at delivery, the risk of hemorrhage dropped noticeably. Similarly, higher levels of transferrin at that moment were linked to a much lower risk of bleeding. The researchers explained that this relationship likely works in reverse: the heavy bleeding itself caused the hemoglobin and transferrin levels to drop, rather than the low levels causing the bleeding. In other words, the blood test taken right after birth reflects the damage that has just happened, not the risk that existed before.

The study also looked at other blood factors, such as platelets, which help blood clot, and ferritin, a measure of iron stores. None of these markers, when measured at 36 weeks, showed a link to the risk of hemorrhage. Even the presence of iron deficiency at that stage did not predict who would bleed heavily. This finding challenges the common assumption that simply treating anemia during pregnancy will automatically prevent hemorrhage, at least in the context of women who are already receiving iron therapy. The results suggest that while anemia is a serious condition with many risks, it may not be a strong, independent predictor of bleeding risk in the way previously thought, especially when the timing of the measurement is taken into account.

The researchers concluded that the timing of a blood test matters immensely when trying to understand the risks of childbirth. A test taken weeks before delivery tells a different story than one taken moments after. The findings highlight that while low blood counts at delivery are a strong sign of a hemorrhage, they are not necessarily a warning sign that can be used to predict the event before it happens. This distinction is crucial for doctors and public health officials, as it suggests that looking at prenatal blood levels alone may not be enough to identify women who will face a bleeding emergency. Instead, the focus may need to shift toward monitoring women closely during labor and immediately after birth, where the signs of hemorrhage become clear. The study underscores the need for more research to understand exactly how and when blood changes during pregnancy influence the risk of bleeding, ensuring that mothers receive the right care at the right time.