Risk Factors for Atonic Postpartum Hemorrhage: A Systematic Review and Meta-analysis

Abstract

Objective: To identify and quantify risk factors for atonic postpartum hemorrhage.

Data sources: PubMed, CINAHL, EMBASE, Web of Science, and and ClinicalTrials.gov databases were searched for English language studies with no restrictions on date or location. Studies included randomized trials, prospective or retrospective cohort studies, and case-control studies of pregnant patients who developed atonic postpartum hemorrhage and reported at least one risk factor.

Methods of study selection: Title, abstract, and full-text screening were performed using the Raayan web application. Of 1,239 records screened, 27 studies were included in this review. Adjusted or unadjusted odds ratios (ORs), relative risks, or rate ratios were recorded or calculated. For each risk factor, a qualitative synthesis of low and moderate risk of bias studies classifies the risk factor as definite, likely, unclear, or not a risk factor. For risk factors with sufficiently homogeneous definitions and reference ranges, a quantitative meta-analysis of low and moderate risk of bias studies was implemented to estimate a combined OR.

Tabulation, integration, and results: Forty-seven potential risk factors for atonic postpartum hemorrhage were identified in this review, of which 15 were judged definite or likely risk factors. The remaining 32 assessed risk factors showed no association with atonic postpartum hemorrhage or had conflicting or unclear evidence.

Conclusion: A substantial proportion of postpartum hemorrhage occurs in the absence of recognized risk factors. Many risk factors for atonic hemorrhage included in current risk-assessment tools were confirmed, with the greatest risk conferred by prior postpartum hemorrhage of any etiology, placenta previa, placental abruption, uterine rupture, and multiple gestation. Novel risk factors not currently included in risk-assessment tools included hypertension, diabetes, and ethnicity. Obesity and magnesium were not associated with atonic postpartum hemorrhage in this review.

Systematic review registration: PROSPERO, CRD42020157521.

Fig. 1.

Flow diagram of studies identified for systematic review. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.

Fig. 2.

Risk of bias assessment. Risk of bias assessments were performed using the Risk of Bias Assessment Tool for Nonrandomized Studies. Green (+) indicates low risk of bias, blue (?) indicates unclear risk of bias, and red (X) indicates high risk of bias. For the summary of risk of bias, studies were considered overall low risk of bias (green +) if they were classified as low risk in all six domains. Studies were considered a moderate risk of bias (yellow —) if at least one domain was rated unclear risk (but no domains were rated high risk) and high risk (red X) if at least one domain was rated high risk. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.

Fig. 3.

Meta-analysis of history and demographic risk factors. Forest plots of odds ratios (ORs) that were included in the quantitative meta-analysis and the associated overall ORs. For each OR, the size of the gray square region is proportional to the corresponding study weight. Diamond-shaped intervals represent the overall ORs. I² represents the fraction of variability among the individual ORs that cannot be explained by sampling variability. aOR, adjusted odds ratio; uOR, unadjusted odds ratio; aRR, adjusted relative risk; PPH, postpartum hemorrhage; CD, cesarean delivery. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.

Fig. 4.

Meta-analysis of maternal comorbidity risk factors. Forest plots of odds ratios (ORs) that were included in the quantitative meta-analysis and the associated overall ORs. For each OR, the size of the gray square region is proportional to the corresponding study weight. Diamond-shaped intervals represent the overall ORs. I² represents the fraction of variability among the individual ORs that cannot be explained by sampling variability. aOR, adjusted odds ratio; uOR, unadjusted odds ratio; aRR, adjusted relative risk; uRR, unadjusted relative risk. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.

Fig. 5.

Meta-analysis of pregnancy-related risk factors. Forest plots of odds ratios (ORs) that were included in the quantitative meta-analysis and the associated overall ORs. For each OR, the size of the gray square region is proportional to the corresponding study weight. Diamond-shaped intervals represent the overall ORs. I² represents the fraction of variability among the individual ORs that cannot be explained by sampling variability. aOR, adjusted odds ratio; aRR, adjusted relative risk; uRR, unadjusted relative risk. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.

Fig. 6.

Meta-analysis of labor-related risk factors. Forest plots of odds ratios (ORs) that were included in the quantitative meta-analysis and the associated overall ORs. For each OR, the size of the gray square region is proportional to the corresponding study weight. Diamond-shaped intervals represent the overall ORs. I² represents the fraction of variability among the individual ORs that cannot be explained by sampling variability. aOR, adjusted odds ratio; uOR, unadjusted odds ratio; aRR, adjusted relative risk; uRR, unadjusted relative risk. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.

Fig. 7.

Meta-analysis of delivery-related risk factors. Forest plots of odds ratios (ORs) that were included in the quantitative meta-analysis and the associated overall ORs. For each OR, the size of the gray square region is proportional to the corresponding study weight. Diamond-shaped intervals represent the overall ORs. I² represents the fraction of variability among the individual ORs that cannot be explained by sampling variability. aOR, adjusted odds ratio; aRR, adjusted relative risk; uRR, unadjusted relative risk. Ende. Atonic Hemorrhage Risk Systematic Review. Obstet Gynecol 2021.