This study is the first, to our knowledge, to document the factors that modulate the course from simple to severe PPH. Our results suggest that various specific characteristics are independent determinants of PPH aggravation. These include the woman’s obstetric history, aspects of delivery before PPH, delay in initial care for PPH, and hospital status.
We found that several characteristics of the woman and her pregnancy, previously described as risk factors for PPH,16–18
also are associated with a higher risk of severity once PPH has occurred. Although any PPH requires immediate management, for women with a history of PPH or cesarean, or having a first baby, or whose labor was managed with induced cervical ripening or was prolonged, or who had an episiotomy, excessive but not severe postpartum bleeding requires even more careful attention because they are at higher risk of severe hemorrhage. Interestingly, several of these characteristics -previous cesarean, cervical ripening, and episiotomy- are related to the management of labor and delivery, and the associations found here provide additional evidence to be considered in balancing the risks and benefits of those procedures. In our cohort of 4550 women with PPH, 2314 (51%) had at least one of these 3 characteristics; efforts to decrease the rate of these procedures may actually reduce the importance of this group and possibly the incidence of severe PPH.
Interestingly, episiotomy is associated with a higher risk of severe PPH, although the study population was restricted to PPH due to uterine atony, with PPH due to bleeding episiotomy excluded. This finding suggests that the existence of multiple sources of blood loss, even in physiological range, increases the risk of severe PPH and reinforces the relevance of policies for limited use of episiotomy at vaginal birth.
An unexpected result was the increased risk of severe PPH in women who received preventive oxytocin, as compared to women with PPH who had no prophylaxis. This may reflect an indication bias, prophylaxis being more likely in women with risk factors, although these risk factors were taken into account in our analysis. Alternatively, excessive postpartum bleeding occurring after and despite prevention may be more likely to be severe, since, by definition, prophylactic oxytocin was not able to prevent it. Another possible explanation is that the surveillance of postpartum blood loss may be less intense when prophylaxis has been done, leading to delayed diagnosis.
Epidural anesthesia had a protective effect here. It has previously been discussed as a risk factor for PPH,17, 22
presumably by lengthening labor or negatively affecting the endogenous oxytocin level or both, but evidence for such an effect is weak so far. Our results suggest that regardless of the effect of the epidural on the occurrence of PPH, women diagnosed with PPH who already have an epidural are at a smaller risk of severe bleeding. This unexpected result illustrates the importance of analyzing the role of risk factors at different levels of the continuum of severity. The presence of the epidural catheter likely facilitates immediate management of PPH since some procedures, such as examination of the uterine cavity, manual removal of the placenta, or instrumental examination of the vagina and cervix, are usually done under anesthesia. Inversely, the need for anesthesia may delay initial care for PPH and thus increase the risk of severe PPH in women who delivered without epidural: in our study population, this group had a significantly higher proportion of women with no or delayed examination of the uterine cavity than did the women with epidurals.
Delay in initial PPH care (manual examination of the uterine cavity, oxytocin administration, and call for extra help) was associated with an increased risk of severe PPH. These results might appear expected or even obvious. However, gathering evidence to support clinical practice recommendations is the principle of evidence-based medicine and an essential task, for it increases their level of proof and thus their legitimacy, both factors that may improve their translation into practice.23
The content of PPH-related guidelines for the initial steps is very similar in all countries. The present study is the first, to our knowledge, to provide evidence to support the recommendations for immediate management of excessive bleeding.
The risk of severe blood loss is higher for women with a PPH after vaginal birth in public non-university hospitals, compared with other public university or private hospitals, and this excess risk is not explained by characteristics of the women, their delivery, or the initial PPH management. We hypothesize that second-line treatment for PPH may be inappropriate or delayed in these hospitals because of limited human (e.g., available staff, surgical skills of obstetricians) or material (e.g., interventional radiology) resources. However, these further steps of PPH management are less standardized and their appropriateness is more difficult to assess because the corresponding content of guidelines is quite imprecise. That is why they were not considered in this study.
The design of the present study had several strengths. It was population-based, covering all maternity units and consequently all deliveries in a given area. This feature ensures the external validity of its results. The prospective identification of deliveries with PPH and the characterization of severe PPH within the cohort of women with identified PPH provided unbiased comparison groups with regard to the study objectives. The large number of units and deliveries provided good power for studying the independent role of multiple factors and allowed an analysis that could take the hierarchical structure of the data into account and explore the role of factors at the levels of both the women and the units. Finally, the definition of severe PPH was based on change in hemoglobin, a more objective criterion than the clinically assessed volume of blood loss, or the need for surgery, embolization, or transfusion, all dependent on practices likely to vary widely among clinicians and centers.
Our definition of severe PPH also has some limitations. Peripartum change in hemoglobin may not always accurately reflect postpartum blood loss. It may overestimate blood loss in women who received large amounts of fluids, who could then be wrongly classified as severe PPH; it may underestimate the total blood loss if not performed after 48 hours of delivery. This is however unlikely to bias our conclusions, as the consequence would actually be an underestimation of the strength of the associations we found with severe PPH. Given our study objectives and the constraints of our data, the definition of severe PPH by a maximum change in Hb appeared as the least biased option.
Selection by indication bias is common in observational studies assessing the role of procedures or treatments on health outcomes. In the present study, some women with PPH may have received more appropriate immediate management because their bleeding was considered at high risk of immediate aggravation. Conversely, in women with excessive bleeding after delivery but not considered to be at risk for heavy blood loss, delay in adequate management is more likely. The effect of this bias is to attenuate the negative impact of inadequate care. The actual associations between delayed initial care and severe PPH may therefore be stronger than we found here. As mentioned above, this bias probably also explains the apparent lower risk of severe PPH in cases where an obstetrician or anesthesiologist were not called promptly.
We cannot exclude the possibility that some procedures were performed but not recorded in the medical files, although this seems unlikely for pharmacological treatments such as oxytocin or invasive exams such as examination of the uterus. The relatively high proportion of missing data for the timing of oxytocin administration and manual examination shows that the quality of data recording in obstetrics files needs to improve. We found that the women with PPH for whom these two procedures were done, but at an unknown time, were at lower risk of severe PPH. One possible explanation for this finding is that the procedures were performed immediately after PPH diagnosis and that the specific time was not recorded because implicitly considered simultaneous with the diagnosis.
Identifying factors that influence the course of PPH from simple to severe has direct potential implications for clinicians, especially for factors related to care, which have been rarely explored so far. Our study shows that some aspects of the management of labor and delivery, as well as delayed initial care for PPH, and place of delivery, increase the risk of heavy postpartum bleeding caused by atony. More specifically, it provides evidence suggesting that reducing the use cervical ripening, episiotomy, or cesarean delivery, in particular in situations where these interventions do not provide clear benefits, as well improving the rapidity of first care once PPH has occurred, may reduce the incidence of severe PPH.