Key messages
• Our study found that using visual estimation to diagnose postpartum haemorrhage (PPH) was inaccurate. Using a plastic drape to collect and measure the volume of blood loss – alongside observations including heart rate, blood pressure, tone of the womb, and flow of blood – showed high accuracy.
• Other tests, including blood tests and measurements such as heart rate and blood pressure alone, showed varying levels of accuracy.
What is postpartum haemorrhage (PPH)?
The World Health Organization defines PPH as blood loss of 500 mL or more in the first 24 hours after delivery in women who gave birth vaginally. Severe PPH is when 1000 mL or more of blood is lost in the same time period.
Why is an accurate diagnosis of PPH important?
PPH is the commonest cause of mothers dying worldwide. Accurately diagnosing it can help in early treatment.
What are the tests used to diagnose PPH?
The commonest test used to diagnose PPH and severe PPH is visual estimation, where a birth attendant estimates the volume of blood lost by looking at the extent to which bedsheets and pads are soaked with blood. Other tests include measuring the volume of blood lost using a plastic drape, tray or bowl with markings indicating the volume. Blood can also be collected and weighed. This weight is converted to a volume using a formula. Other tests include measuring changes in (1) the levels of certain chemicals in the birthing woman's blood, or (2) variables such as her heart rate and blood pressure.
What did we want to find out?
We wanted to identify different tests and methods used to diagnose PPH and severe PPH and find out how accurate they are.
What did we do?
We looked for studies that assessed the accuracy of tests used to diagnose PPH and severe PPH when compared with a reliable standard such as weighed blood loss or the measured volume of blood loss. Women of any age who gave birth vaginally in any setting (hospitals, delivery units in the community, home births) were included.
We included studies which provided data that we could use to determine two measures of test accuracy: (1) sensitivity (percentage of women with the condition who are correctly identified by the test); and (2) specificity (percentage of women without the condition who are correctly excluded by the test). Where appropriate, we combined the results across these studies. We excluded studies that did not provide this type of information.
Examples of tests we looked for included the assessor: looking at the blood loss and estimating the blood volume (visual estimation); measuring the volume of blood loss in a drape or other collecting device with markings indicating the volume (volumetric method); weighing blood loss using scales (gravimetric method); measuring changes in variables such as heart rate and blood pressure, or changes in blood levels of chemicals such as haemoglobin and fibrinogen. We also tried to find studies which combined the tests mentioned above and tests using new technologies such as camera systems and artificial intelligence.
What did we find?
We found 18 studies with a total of 291,040 participants.
Fourteen studies assessed diagnostic tests for PPH and seven studies assessed tests for severe PPH. Most of the studies were performed in hospitals.
Visual estimation had poor sensitivity. In one of our analyses, we found that visual estimation will only diagnose 48 out of 100 women who have PPH, but 52 women with PPH will be missed (i.e. will be false negatives). These missed cases may not receive treatment and so may suffer avoidable harm and may even die. Of every 100 women without PPH, three will be wrongly diagnosed as having it (i.e. will be false positives). These incorrectly diagnosed women may receive treatment which they don't require and may suffer harm as a result.
A diagnostic approach which used a calibrated drape to measure the volume of blood loss, along with observations such as heart rate, blood pressure, the tone of the womb, and flow of blood to diagnose PPH had very good sensitivity and specificity. Using this approach will diagnose 93 out of 100 women who have PPH, and only seven women with PPH will be missed (i.e. will be false negatives). Of every 100 women without PPH, five will be wrongly diagnosed as having it (i.e. will be false positives).
Other tests showed varying levels of accuracy for diagnosing PPH and severe PPH.
What are the limitations of the evidence?
The studies we found were mainly performed in hospitals. We would have liked more information on how accurate the tests are in other settings, such as in the community and at home.
We would also have liked to know how accurate the other tests are when used in combination, particularly the combination of measured blood loss, changes in factors such as heart rate and blood pressure, and changes in blood chemical levels.
How current is this evidence?
This evidence is current to 24 May 2024.
Visual estimation of blood loss to diagnose PPH showed low sensitivity and is likely to miss the diagnosis in half of women giving birth vaginally. A diagnostic approach using a calibrated drape to objectively measure blood loss plus clinical observations showed high sensitivity and specificity for diagnosing PPH. Other index tests showed low to moderate sensitivities in diagnosing PPH and severe PPH.
Future research should determine the accuracy of diagnostic tests in non-hospital settings and consider combining index tests to increase the sensitivity of PPH diagnosis.
Postpartum haemorrhage (PPH) is the leading cause of maternal mortality worldwide. Accurate diagnosis of PPH can prevent adverse outcomes by enabling early treatment.
What is the accuracy of methods (index tests) for diagnosing primary PPH (blood loss ≥ 500 mL in the first 24 hours after birth) and severe primary PPH (blood loss ≥ 1000 mL in the first 24 hours after birth) (target conditions) in women giving birth vaginally (participants) compared to weighed blood loss measurement or other objective measurements of blood loss (reference standards)?
We searched CENTRAL, MEDLINE, Embase, Web of Science Core Collection, ClinicalTrials.gov, and the World Health Organization International Clinical Trials Registry Platform to 24 May 2024.
We included women who gave birth vaginally in any setting. Study types included diagnostic cohort studies and cross-sectional studies that reported 2 x 2 data (number of true positive, false positive, false negative, and true negative results) or where the 2 x 2 data could be derived from test accuracy estimates.
Eligible index tests included: visual estimation; calibrated blood collection devices; approach with calibrated drape and observations; blood loss estimation using the SAPHE (Signalling a Postpartum Hemorrhage Emergency) Mat; blood loss field image analysis and other technologies; uterine atony assessment; clinical variables (e.g. heart rate, blood pressure, shock index); early warning charts; haemoglobin levels; and predelivery fibrinogen levels.
Eligible reference standards included objective methods such as: gravimetric blood loss measurement, which involves weighing collected blood, as well as weighing blood-soaked pads, gauze and sheets, and subtracting their dry weight; calibrated devices to measure blood volume (volumetric blood loss measurement); the alkaline-haematin method of blood loss estimation; and blood extracted using machine-extraction and measured spectrometrically as oxyhaemoglobin.
At least two review authors, working independently, undertook study screening, selection, data extraction, assessment of risk of bias, and assessment of the certainty of the evidence. We resolved any differences through consensus or with input from another author.
We generated 2 x 2 tables of the true positives, true negatives, false positives, and false negatives to calculate the sensitivity, specificity, and 95% confidence intervals for each index test. We presented sensitivity and specificity estimates from studies in forest plots. Where possible, we conducted meta-analyses for each index test and reference standard combination for each target condition.
We examined heterogeneity by visual inspection of the forest plots.
Our review included 18 studies with a total of 291,040 participants. Fourteen studies evaluated PPH and seven studies evaluated severe PPH. Most studies were conducted in a hospital setting (16 of 18).
There were four studies at high risk of bias for the patient selection domain and 14 studies at low risk. For the index test domain, 10 studies were at low risk of bias, seven studies at high risk, and one study at uncertain risk. For the reference standard domain, one study was at high risk of bias and 17 studies at low risk. For the flow and timing domain, three studies were at high risk of bias and 15 studies at low risk. The applicability concerns were low for all studies across the domains.
In the abstract, we have prioritised reporting results for common, important thresholds for index tests or where the certainty of the evidence for the sensitivity estimate was at least moderate. Full results are in the main body of the review.
PPH (blood loss ≥ 500 mL)
For PPH, visual estimation with gravimetric blood loss measurement as the reference standard had 48% sensitivity (95% confidence interval (CI) 44% to 53%; moderate certainty) and 97% specificity (95% CI 95% to 99%; high certainty) (4 studies, 196,305 participants).
Visual estimation with volumetric blood loss measurement as the reference standard showed 22% sensitivity (95% CI 12% to 37%; moderate certainty) and 99% specificity (95% CI 97% to 100%; moderate certainty) (2 studies, 514 participants).
The diagnostic approach with calibrated drape plus observations, with gravimetric blood loss measurement as the reference standard for PPH, showed 93% sensitivity (95% CI 92% to 94%; high certainty) and 95% specificity (95% CI 95% to 96%; high certainty) (2 studies, 53,762 participants).
A haemoglobin level of less than 10 g/dL with gravimetric blood loss measurement as the reference standard showed 37% sensitivity (95% CI 30% to 44%; high certainty) and 79% specificity (95% CI 76% to 82%; high certainty) (1 study, 1058 participants).
Severe PPH (blood loss ≥ 1000 mL)
For severe PPH, visual estimation, with volumetric plus gravimetric blood loss measurement as the reference standard, showed 9% sensitivity (95% CI 0% to 41%; low certainty) and 100% specificity (95% CI 99% to 100%; moderate certainty) (1 study, 274 participants).
A shock index level of 1.0 or higher (commonly used as a threshold for severe PPH) up to two hours after birth, with gravimetric blood loss measurement as the reference standard, showed 30% sensitivity (95% CI 27% to 33%; moderate certainty) and 93% specificity (95% CI 92% to 93%; moderate certainty) (1 study, 30,820 participants).
A haemoglobin level of less than 10 g/dL, with gravimetric blood loss measurement as the reference standard, showed 71% sensitivity (95% CI 51% to 87%; moderate certainty) and 77% specificity (95% CI 75% to 80%; high certainty) (1 study, 1058 participants).
Bill and Melinda Gates Foundation
PROSPERO (CRD42024541874)