Nataly’s Knowledge Hub
Questions, evidence and clinical experience on postpartum hemorrhage and maternal health.
Why is blood loss so hard to estimate after birth?
Blood loss after birth is hard to estimate because it is almost always judged by eye, and the human eye is unreliable at this particular task. According to the 2025 Cochrane review of diagnostic tests for postpartum hemorrhage, visual estimation detects only 48% of cases at vaginal birth. The difficulty is not a matter of attention or skill. Blood after birth is diluted with other fluids, absorbed into materials that hide it, and spread across several surfaces at the same time, which makes accurate judgement by sight close to impossible.
How accurate is visual estimation of blood loss?
Visual estimation detects 48% of postpartum hemorrhages at vaginal birth, with 97% specificity, according to the 2025 Cochrane review of diagnostic tests for postpartum hemorrhage. A calibrated drape combined with clinical observations detects 93% of cases, with 95% specificity, in the same review.
In severe hemorrhage the gap widens sharply. The Cochrane review reports that visual estimation detects 9% of severe postpartum hemorrhages, meaning it misses more than nine cases in ten at the point where the risk to the woman is greatest.
Those two figures, 48% against 93%, describe the same moment and the same woman assessed by two different methods. The difference is not the clinician: it is whether the blood is looked at or measured.
Why does visual estimation of blood loss fail?
Visual estimation of blood loss fails for four reasons that act at the same time, and the resulting error is systematic rather than random. Small volumes are consistently overestimated and large ones underestimated, with the percentage error growing as the true volume grows, which means the method fails most when the loss matters most.
Blood after birth is never in one place. It is on the pad, the underpad, the sheets and the floor, and nobody adds up volumes spread across separate surfaces accurately just by looking at them. It is also mixed with amniotic fluid, urine, antiseptics and saline, so what is visible is blood diluted in an unknown proportion rather than blood itself.
Absorbent materials compound the problem, because they hide volume by design: a soaked pad looks the same whether it holds 100 mL or 250 mL. And human perception responds to the surface area of a stain rather than its contents, so a loss spread thinly across a sheet looks far larger than the same volume pooled in one place.
Does experience improve visual estimation of blood loss?
Experience does not reliably improve the accuracy of visual estimation of blood loss, although the opposite is widely taught. A study at a London teaching hospital that measured accuracy and reproducibility among health- care professionals concluded that experience did not appear to affect accuracy, and found that small volumes were overestimated by up to 540% while two estimates of the same volume by the same person could differ by 300%.
A second study in a different population compared visual estimation with gravimetric measurement and found a mean underestimation of around 30%. In that study, neither prior training nor the seniority of the professional affected the accuracy of the estimate.
The evidence on whether targeted training helps is contradictory: some studies report improvement after simulation-based teaching and others find none. What no study supports is the idea that accumulated experience on its own corrects the bias. The conclusion is not that experienced clinicians are poor clinicians, but that the task cannot be done well by looking.
What is estimating blood loss like in practice?
At university I was taught to estimate using pads: one soaked pad is roughly 200 mL. It gives you something to hold on to, but it is a rough figure and it depends on what is actually in there. We were also told that clinical judgement sharpens with the years.
I was once attending a birth and the third stage with another midwife beside me. She asked me whether I thought that amount of blood was normal. I could see it was more bleeding than usual, but I did not have enough reference points to know I was looking at a postpartum hemorrhage. She did, and she told me to start the protocol.
What I missed most was the language. People said “a lot” or “a little” blood. It would have helped me enormously if estimated millilitres had been said out loud, even approximate ones, so I could build a reference in my head. You cannot build a reference from “a lot”.
And there is something I learned by watching rather than by studying: what comes out is not only blood. It is amniotic fluid, it is placenta, it is several things at once. Estimating well means judging consistency, working out how much amniotic fluid is in there, and looking at the woman’s hemodynamic state at the same time. Nobody explained that to me before I walked into a delivery room for the first time.
Catalina Díaz Jiménez, midwife
How much blood loss counts as a postpartum hemorrhage?
There is no single definition of postpartum hemorrhage, and the threshold depends on which guideline is being used. The World Health Organization classically defined it as a loss of 500 mL or more at vaginal birth, or 1000 mL or more at cesarean section.
The American College of Obstetricians and Gynecologists defines postpartum hemorrhage as a cumulative loss of 1000 mL or more, or any blood loss accompanied by signs of hypovolemia within the first 24 hours, regardless of how the woman gave birth. ACOG also notes that a loss above 500 mL should raise concern in any birth, and that context matters: pre- existing anemia or low body weight change what a given volume means.
Since October 2025, the consolidated guidelines published jointly by WHO, FIGO and the International Confederation of Midwives recommend acting on a measured loss of 300 mL or more when it occurs together with any abnormal vital sign. The reasoning behind the change is explicit: lowering the threshold for action is safer than waiting for the classic criterion to be met, because by the time it is met, treatment often begins too late.
How is blood loss measured objectively after birth?
Blood loss after birth is measured objectively in two ways, both of which replace judgement with a number. Gravimetric measurement involves weighing soaked materials and subtracting their dry weight, where one gram of difference corresponds to approximately one millilitre of blood; it is inexpensive and accurate, and requires only a scale and the discipline to use it.
The second method is a calibrated drape, a graduated plastic device placed under the woman that collects blood and measures it directly against printed volume markings. This is the objective method recommended in the 2025 WHO, FIGO and ICM consolidated guidelines, and the one used in the E- MOTIVE trial.
Whichever method is used, the measurement has to be cumulative rather than a single figure recorded at the end. Late diagnosis of postpartum hemorrhage frequently comes from assessing separate volumes in isolation instead of tracking a running total that grows over time.
Why does accurate measurement of blood loss matter?
Accurate measurement of blood loss matters because the treatments for postpartum hemorrhage already exist, are inexpensive and work: oxytocin, tranexamic acid, uterine massage, intravenous fluids and examination of the birth canal are all widely available. The obstacle is not treatment but recognition.
Women die from a condition that clinicians know how to treat, largely because it is identified too late. And it is identified too late in part because the dominant method of detection for decades has been to look at the blood rather than to measure it.
Can you have a postpartum hemorrhage with normal vital signs?
Yes, and in the early stages it is the norm. A young, healthy woman can lose a significant volume of blood while her blood pressure stays within the normal range, because her body compensates for the loss before any measurement changes.
This is why the 2025 WHO, FIGO and ICM guidelines do not rely on vital signs alone. Normal vital signs after birth do not rule out an ongoing hemorrhage; they confirm that the woman is still compensating for it.
Why can a woman lose a lot of blood with normal blood pressure?
A woman can lose a large volume of blood with normal blood pressure because pregnancy substantially increases circulating blood volume, and that expansion functions as a reserve which exists precisely so the body can tolerate the blood loss of childbirth.
Added to that reserve is the acute response to hypovolemia. Vasoconstriction and a rise in heart rate keep arterial pressure stable for as long as the body can sustain them, which produces a period in which the woman is actively bleeding and the numbers on the monitor still look normal.
This is not a failure of monitoring but physiology working as it should. The clinical problem is that when compensation runs out, it does not run out gradually.
Which signs of postpartum hemorrhage appear first?
In postpartum hemorrhage, symptoms usually appear before measurable signs. Restlessness with no obvious cause, anxiety, breathlessness, feeling cold and a vague sense of being unwell frequently precede any change in vital signs, and in severe obstetric hemorrhage they are often the earliest indication that something is wrong.
Heart rate changes next, rising before blood pressure falls. Blood pressure is the latest marker of all, which leads to an uncomfortable practical conclusion: waiting for the blood pressure to drop before treating a woman as unwell means arriving late by design.
Should the threshold for action be based on volume, on vital signs, or on both?
The threshold for action in postpartum hemorrhage should be based on both volume and vital signs together, because each performs poorly on its own. A WHO individual participant data meta-analysis covering twelve datasets and 312,151 women assessed which clinical markers best predict maternal death or severe morbidity, and the results explain why the guideline changed in 2025.
Using the classic threshold of 500 mL, sensitivity was 75.7% and specificity 81.4%. Lowering the threshold to 300 mL raised sensitivity to 83.9% but dropped specificity to 54.8%, meaning far more women would be treated as bleeding heavily when they were not.
Combining the two performed better than either alone. A rule based on 300 to 450 mL together with any abnormal hemodynamic sign, or 500 mL regardless of signs, reached a sensitivity of 86.9% to 87.9% with a specificity of 66.6% to 76.1%. This is why the 2025 recommendation is written with an “and” rather than an “or”.
What counts as an abnormal vital sign after birth?
The WHO individual participant data meta-analysis that underpins the 2025 threshold defines four abnormal hemodynamic signs in the postpartum period. They are a heart rate above 100 beats per minute, a systolic blood pressure below 100 mmHg, a diastolic blood pressure below 60 mmHg, and a shock index above 1.0.
Any one of those four, occurring together with a measured blood loss of 300 mL or more, is the trigger for action under the 2025 WHO, FIGO and ICM guidelines.
What is the shock index and why does it matter in obstetrics?
The shock index is heart rate divided by systolic blood pressure, and it matters in obstetrics because it detects hemodynamic deterioration before either of those two parameters becomes alarming on its own. In healthy adults the normal range is reported as 0.5 to 0.7.
Values in the immediate postpartum period differ slightly. A study published in PLOS ONE in 2016 established a median shock index of 0.66 in women during the first hour after birth with an estimated loss under 500 mL, with a 90% reference range between 0.52 and 0.89.
Since 2025 the shock index also has a formal role in diagnosis, since a value above 1.0 is one of the four abnormal hemodynamic signs recognised by WHO. Its practical advantage is that it requires no equipment beyond what is already being measured.
What do midwives watch beyond the numbers?
We did use the shock index. It is something midwives keep in mind.
But if I had to say one thing to someone starting their placements, it would be this: vital signs matter enormously, and even so, the most important thing is to look at the woman’s face. Her physical state, her level of consciousness. The whole picture, not just the numbers on a screen.
Because every patient is different. The textbook says one thing, but situations do not unfold like a checklist. You have to know how to act when you are sure, and also when you are acting just in case. The patient’s life is worth more than the theory.
Catalina Díaz Jiménez, midwife
What is checked in the first hours after birth?
The World Health Organization recommends routine assessment of vaginal bleeding, uterine tone, fundal height, temperature and heart rate during the first 24 hours after birth, beginning in the first hour. Blood pressure is measured shortly after birth and, if normal, repeated within six hours, and the first urine void is documented within the same period.
That list is a minimum designed to be achievable in any health system in the world, including those with very limited resources, which is why it defines what must be done rather than what good practice looks like. In practice a midwife’s assessment goes considerably further.
What does a midwife check after birth?
What I was taught to do in the postpartum period was a full physical examination, general and segmental, always in the same order. Start with hemodynamic status: vital signs, temperature, blood pressure, heart rate, oxygen saturation. Then mucous membranes, to assess hydration. Limbs. Check the IV line was patent. Breasts, colostrum, how the newborn latched. Abdomen. Uterus: assess retraction, press and see how much blood came out with that maneuver, and perform uterine massage if involution was not adequate. Genitals, the state of any sutures, and the smell of the lochia.
The order matters more than you would think when you are learning it. It is not a list of things to touch: it is a sequence that forces you to look at the whole woman before you look at her uterus.
Catalina Díaz Jiménez, midwife
When is the risk of postpartum hemorrhage highest?
The risk of postpartum hemorrhage is highest in the first hour after birth. According to WHO, around 50% of maternal deaths occur within the first 24 hours following delivery, and within that window the risk is not evenly distributed: massive hemorrhage tends to occur in the first hour, and most hemorrhage deaths within the first two to three hours.
Because of that concentration, a “golden 90 minutes” frame has been proposed for the diagnosis of postpartum hemorrhage, a far tighter window than the 24 hours usually cited.
How often should a woman be checked after birth?
WHO recommends four assessments during the first hour after birth and regular monitoring throughout the first 24 hours, but it does not define how often “regular”; means beyond that first hour. The operational definition is left to local protocols, and those protocols arrive at very different answers.
Reported intervals range from checks every 15 minutes for the first two hours in intensive monitoring protocols, to a two-phase scheme in which bleeding and uterine retraction are monitored hourly while the woman remains in the recovery room, and then every six to eight hours once she moves to the postnatal ward. All of those schedules fit within what WHO calls regular assessment.
Does structured monitoring improve detection of postpartum hemorrhage?
Structured monitoring substantially improves the detection of postpartum hemorrhage. An observational study nested within the E-MOTIVE trial found that hospitals applying structured assessments diagnosed 76% of hemorrhages within the first 30 minutes after birth, compared with 54% in hospitals delivering usual care.
The structured protocol involved assessing uterine tone and vaginal flow and quantifying cumulative blood loss objectively every 15 minutes. The improvement did not come from new technology or additional staff: it came from performing the same work in a fixed sequence and against a clock.
When is a woman least monitored after giving birth?
A woman is least monitored during the transition from the recovery room to the postnatal ward, when the interval between assessments typically moves from hourly to every six or eight hours. The same woman, on the same day, goes from being checked every sixty minutes to being checked three times in a day.
This is not a flaw in the protocols. The greatest risk is genuinely concentrated in the first hours, and no health system can sustain hourly observation for three days. But it means a hemorrhage that begins shortly after one check has a wide margin before anyone looks again, and it is the point at which the sensitivity of the whole process drops most sharply.
It is also the moment at which a woman is most alone: no longer in the delivery room, not yet at home. This is one of the reasons the 2025 guidelines and recent trials emphasise objective, cumulative measurement rather than intermittent visual checks.
What causes postpartum hemorrhage?
The causes of postpartum hemorrhage are grouped under a mnemonic known as the four Ts: tone, trauma, tissue and thrombin. Uterine atony, meaning ineffective uterine retraction after birth, is by far the most common and accounts for approximately 90% of cases.
Trauma to the birth canal accounts for around 6%, and its incidence rises with assisted vaginal birth using forceps. Uterine rupture is a much rarer cause within this group and requires a previous uterine scar from a cesarean section or myomectomy. Retained tissue accounts for around 4% and refers to incomplete delivery of the placenta, with fragments of cotyledons or membranes remaining in the uterine cavity; placenta accreta spectrum also causes retention and bleeding. Disorders of hemostasis, whether coagulopathies or platelet function disorders, are an infrequent cause.
The value of the mnemonic lies in the order in which causes are excluded rather than in the list itself. Faced with active bleeding, tone is assessed first because it is the most common cause and the fastest to treat; the birth canal is examined next; and if bleeding persists with adequate tone and no visible trauma, retained tissue has to be considered. That sequence is what turns a list into a procedure.
What is secondary postpartum hemorrhage?
Secondary or late postpartum hemorrhage is excessive bleeding that appears after the first 24 hours following birth, and WHO considers this period to extend to 12 weeks postpartum. It is distinguished from primary postpartum hemorrhage, which occurs within the first 24 hours.
Its most common causes differ from those of primary hemorrhage. Retained placental tissue and uterine infection predominate, rather than the uterine atony that dominates the early hours after birth.
Secondary postpartum hemorrhage has one feature that makes it clinically distinct: in most cases the woman is already at home, without any clinical monitoring. The first judgement about whether her bleeding is normal is made by her, using the information she was given at discharge, which makes that information part of the diagnostic process. It also means the period of real risk lasts far longer than the period of surveillance.
About this content
Written by Catalina Díaz Jiménez, midwife, for Nataly. The content sits within the scope of midwifery practice and is provided for information only; it does not replace assessment by a health professional.
Every claim is drawn from clinical guidelines or peer-reviewed literature, and sources are listed below. Clinical experience described in the first person is identified as such and kept separate from scientific evidence: it illustrates a concept rather than proving one. No patient information is published, and no detail that could identify a patient appears anywhere in this content.
Last reviewed: September 2026. If you find an error, write to us at info@natalylife.com and we will correct it.
Nataly develops technology for the early detection of postpartum hemorrhage.
Sources
Tests for diagnosis of postpartum haemorrhage at vaginal birth. Cochrane Database of Systematic Reviews. 2025;1:CD016134.
World Health Organization, FIGO and the International Confederation of Midwives. Consolidated guidelines for the prevention, diagnosis and treatment of postpartum haemorrhage. Geneva, October 2025.
Prognostic accuracy of clinical markers of postpartum bleeding in predicting maternal mortality or severe morbidity: a WHO individual participant data meta-analysis. 2025.
World Health Organization. Recommendations on maternal and newborn care for a positive postnatal experience. Geneva, 2022.
World Health Organization. Technical Consultation on Postpartum and Postnatal Care. Geneva.
Clinical care processes for early postpartum haemorrhage diagnosis: a nested observational study within the E-MOTIVE trial. Frontiers in Global Women’s Health, 2025.
Yoong W, Karavolos S, Damodaram M, et al. Observer accuracy and reproducibility of visual estimation of blood loss in obstetrics. Archives of Gynecology and Obstetrics. 2010;281(2):207–13.
Al Kadri HMF, et al. Visual estimation versus gravimetric measurement of postpartum blood loss. Archives of Gynecology and Obstetrics. 2011.
Nathan HL, et al. Determination of normal ranges of shock index and other haemodynamic variables in the immediate postpartum period. PLOS ONE, 2016.
Say L, et al. Global causes of maternal death: a WHO systematic analysis. The Lancet Global Health, 2014.
Carvajal JA, García KF. Manual de Obstetricia y Ginecología. 17th ed. Santiago: Pontificia Universidad Católica de Chile; 2026.
