Thirty-six papers were included in the integrative review. They used a range of methodological approaches that are summarised in Table 1. An additional file shows the characteristics of included studies in more detail (See Additional file 2). Twenty-nine quantitative studies are included that tested a range of blood loss evaluation methods (See Table 2). Twenty–four tested the diagnostic accuracy of visual estimation with 16 of these testing strategies aimed at improving the accuracy of estimation. A further 5 studies evaluated a combination of interventions aimed at reducing the incidence of PPH and improving its management. Four studies used a randomised controlled design. Seven qualitative studies were included (See Table 3). Four of these were conducted in low-income settings and explored community perceptions of blood loss. Of the 3 qualitative studies conducted in high-income settings, 2 explored women’s experiences of PPH and PPH-related hysterectomy, and 1 explored midwives’ management of the third stage of labour.

Table 1 Types of research methodology in the 36 included papers Full size table

Table 2 Blood loss evaluation methods tested in the 29 quantitative studies Full size table

Table 3 Phenomena of interest in the 7 qualitative studies Full size table

In 1959 Wilcox et al. [21] used the cyanmethemoglobin photelometric method of measuring blood loss and determined that average blood loss in 25 women undergoing caesarean section was 1028 ml. He noted that in 22 cases the clinical estimate of blood loss was 325 ml less than the laboratory measured values and was overestimated in just 3 cases. The method was described as a ‘time consuming, exacting procedure’ (p535), and although deemed unsuitable for clinical use, was commended for research purposes. Spectrophotometry was subsequently developed as the ‘gold standard’, laboratory-based technique for calculating blood loss. With an error rate of between zero and 10 % it was considered to be a reliable method for quantifying blood loss in the research context [22].

Eight studies [12, 23–29] used spectrophotometry to determine average blood loss at vaginal and caesarean birth. Mean blood losses at uncomplicated vaginal births were reported as 226 ml [28] to 286 ml [12, 29]. Two studies of women, with ‘additional complications’, having elective and emergency caesarean section reported mean blood losses of 1068 ml and 1,106 ml respectively [24, 25]. Later studies of women undergoing elective caesarean section reported a mean blood loss of 487 ml [27] and a median loss of 500 ml [12].

Seven [12, 23–28] of the 8 studies found that visual estimation was inaccurate. One study [23] reported that there was no correlation between estimated and measured loss at vaginal delivery, while 4 studies reported underestimations of between 46 % and 75 % [24–28]. Six out of eight studies confirmed that the extent of underestimation increased as the volume of blood loss increased [23–28]. Two studies [25, 28] reported that estimation was most accurate at low volumes, although there was also a tendency to overestimate small amounts. Only one study [29] found ‘visual estimates’ to be accurate (to within 4.90 ml of the spectrophotometry values). However, the paper described that blood loss was collected 'on a delivery pad… and was then weighed on a scale” (p25), suggesting that the gravimetric method was compared to spectrophotometry, and not visual estimation.

The gravimetric method was used to assess the accuracy of visual estimation in 150 vaginal births and found that visually estimated blood losses were 30 % lower than the gravimetric estimates across all professional groups, irrespective of their levels of experience [30]. Three studies compared changes in maternal haematocrit values to visually estimated blood loss [31–33]. The first study [31] used changes in haematocrit values within a formula for calculating estimated blood loss and found statistically significant underestimation of blood loss in 677 women when using visual estimation. While the second study [32] found that all women with estimated blood loss greater than 500 ml had a decline in their haematocrit at 48 h post-delivery, a third study [33] found that there was a lower incidence of PPH (PPH rate: 8.9 %) when using visual estimation compared to using a fall in maternal haematocrit values (PPH rate: 16.2 %).

Nine studies aimed to improve skills and accuracy in visual estimation through training, education and development of clinical assessment tools [34–42], although none were able to show long term improvements or translation of skills into clinical practice. One study [36] photographed each reconstruction of blood loss to produce a pictorial guide for blood loss assessment although this was not evaluated in clinical practice.

One study evaluating estimations of eight blood loss simulations before and after a PowerPoint presentation on blood loss estimation found that error was reduced in the post-presentation estimates [35]. However, a similar study that found improved blood loss estimates immediately after didactic and web-based training [40] retested the web-based training group after 9 months and found that accuracy of blood loss estimation had deteriorated [42].

A study using high fidelity PPH simulation [39] found that midwives and obstetricians visually underestimated blood loss by 40 % to 49 %. In an intervention aimed at improving the accuracy of estimation, a small number of teams were given verbal instruction to estimate blood loss at set intervals. The accuracy of estimation was found to improve in the intervention groups although blood losses were still underestimated by an average of 32 %. The simulations were videotaped and, at the conclusion of each scenario, played back to participants who discussed their actions. A ‘verbal questionnaire’ was used during the discussion to ask specific questions about PPH management, the answers to which were quantitatively analysed. It was reported that 68 % of participants said they deliberately increased their estimations because they knew that visual estimation underestimated blood loss. A number of participants said that they would consider other parameters when making decisions during PPH such as the haemodynamic stability (34 %) of the woman, laboratory results (42 %) and pad counts (26 %). Many participants described that they used ‘gut feeling’ (60 %) or ‘pure guesswork’ (32 %) to estimate blood loss. Although these comments were not explored any further by the authors of the study, who dismissed them as ‘disturbing’ (p933), they may suggest that factors other than volume are important during decision-making about blood loss.

A small number of qualitative studies suggested that factors other than volume were taken into consideration when making decisions about blood loss. Four studies [43–46] in low income countries included trained and untrained traditional birth attendants, women, their families and community members and one study in a high income country included Swedish midwives [47], described blood loss at birth as being normal to some extent.

“I was taught a little bleeding is normal at this stage” [47] (p613).

While in one study [43] food cans were described as being used to collect and quantify blood loss, all 4 studies in low income settings described ‘abnormal’ or ‘alarming’ blood loss using language that depicted the speed and flow of the blood, rather than the volume:

“A continuous, swift flow or gush… it overflows the place…it comes out with force, gushing like water comes from a tube well” [44] (p355)

Delays in the diagnosis of PPH were also apparent in the low income settings where maternal collapse, loss of consciousness, pallor and cyanosis were used as signs that blood loss was serious [45]. The findings of two studies [48, 49] involving women in the high income settings also highlighted the clear perceptions women have at the time of haemorrhage.

Four studies evaluated guideline compliance and the impact of educational interventions on clinical outcomes [50–53]. Two studies reported only partial compliance with local and regional guidelines which was improved by one author [50] through a programme of focussed training for all staff providing intra-partum care alongside revised guidelines. Similarly, a ‘persistent reduction in the prevalence of severe PPH’ (p583) was reported by an observational study [54] in France, where the management and quality of care in all cases of severe PPH was subject to regular audit. However, the authors stated that it was unclear whether it was regular audit or other unrelated factors (such as global improvements in PPH management or a reduction in the number of women at risk) that had led to the decreased incidence of severe PPH. The remaining two studies [52, 53] used a multifaceted approach to guideline implementation and training with the aim of improving PPH prevention, recognition and management. There were some changes in clinical practices as a result of the interventions. In the first study [52] there was improvement in use of second line uterotonics and escalation of care. In the second study [53] active management of the third stage of labour increased from 58.8 % to 75.9 %, and systematic use of blood collection bags increased from 3.9 % to 76.4 %. However, the incidence of major PPH and initial responses to it were reported to be unchanged and the authors concluded that the impact of blood collection bags on clinical outcomes could not be demonstrated.

Four studies [13, 38, 55, 56] specifically investigated the effect of blood collection bags on the accuracy of blood loss estimation, PPH diagnosis, and PPH management. Calibrated bags were shown to facilitate accurate estimations in both clinical reconstructions [38] and in clinical practice [13]. Patel et al. (2006) [13] compared visual estimates with calibrated blood bag estimates before testing a sub-group of 10 blood collection bags using spectrophotometry. Visual estimates were 33 % lower than the blood bag estimates, 10 of which were verified using spectrophotometry. However, while Patel et al. (2006) showed that blood collection bags provided an accurate assessment of blood loss, a later study [56] of 122 women found that, for blood losses of 500 ml or more, the positive predictive value of the blood collection bag was only 66.7 %. The authors suggested that lowering the diagnostic threshold of PPH to 300 ml may be necessary to improve the diagnostic value of the collection bag. A cluster randomised trial [55] including 25,381 vaginal deliveries in 13 European countries is the largest study to date comparing the use of the blood collection bag to visual estimation. The study proposed that using blood collection bags would facilitate more objective monitoring and measurement of postpartum blood loss than visual assessment, triggering an earlier response from caregivers and thus reducing the incidence of severe PPH. Severe PPH occurred in 189 of the 11,037 vaginal births using blood collection bags in the intervention group (1.71 %); and 295 of the 14,344 vaginal births using visual assessment in the control group (2.06 %). At both individual and cluster level analysis, the difference was not statistically significant and the authors concluded ‘that the systematic use of a collector bag after vaginal delivery did not modify the rate of severe postpartum haemorrhage’. The authors’ offered a number of explanations for what they describe as the ‘negative result’ of their trial, summarised by the statement that,