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Distribution of postpartum blood loss: modeling, estimation and application to clinical trials.

ABSTRACT: BACKGROUND:The loss of large amounts of blood postpartum can lead to severe maternal morbidity and mortality. Understanding the nature of postpartum blood loss distribution is critical for the development of efficient analysis techniques when comparing treatments to prevent this event. When blood loss is measured, resulting in a continuous volume measure, often this variable is categorized in classes, and reduced to an indicator of volume greater than a cutoff point. This reduction of volume to classes entails a substantial loss of information. As a consequence, very large trials are needed to assess clinically important differences between treatments to prevent postpartum haemorrhage. METHODS:The authors explore the nature of postpartum blood loss distribution, assuming that the physical properties of blood loss lead to a lognormal distribution. Data from four clinical trials and one observational study are used to confirm this empirically. Estimates of probabilities of postpartum haemorrhage events 'blood loss greater than a cutoff point' and relative risks are obtained from the fitted lognormal distributions. Confidence intervals for relative risk are obtained by bootstrap techniques. RESULTS:A variant of the lognormal distribution, the three-parameter lognormal distribution, showed an excellent fit to postpartum blood loss data of the four trials and the observational study. A measurement quality assessment showed that problems of digit preference and lower limit of detection were well handled by the lognormal fit. The analysis of postpartum haemorrhage events based on a lognormal distribution improved the efficiency of the estimates. Sample size calculation for a hypothetical future trial showed that the application of this procedure permits a reduction of sample size for treatment comparison. CONCLUSION:A variant of the lognormal distribution fitted very well postpartum blood loss data from different geographical areas, suggesting that the lognormal distribution might fit postpartum blood loss universally. An approach of analysis of postpartum haemorrhage events based on the lognormal distribution improves efficiency of estimates of probabilities and relative risk, and permits a reduction of sample size for treatment comparison. TRIAL REGISTRATION:This paper reports secondary analyses for trials registered at Australian New Zealand Clinical Trials Registry (ACTRN 12608000434392 and ACTRN12614000870651); and at clinicaltrials.gov (NCT00781066).

SUBMITTER: Carvalho JF

PROVIDER: S-EPMC6280488 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature

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Distribution of postpartum blood loss: modeling, estimation and application to clinical trials.

Carvalho José Ferreira de JF Piaggio Gilda G Wojdyla Daniel D Widmer Mariana M Gülmezoglu A Metin AM

Reproductive health 20181204 1

<h4>Background</h4>The loss of large amounts of blood postpartum can lead to severe maternal morbidity and mortality. Understanding the nature of postpartum blood loss distribution is critical for the development of efficient analysis techniques when comparing treatments to prevent this event. When blood loss is measured, resulting in a continuous volume measure, often this variable is categorized in classes, and reduced to an indicator of volume greater than a cutoff point. This reduction of vo ...[more]

PMID: 30514326

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Project description:Aims and objectivesThis study aimed at evaluating the accuracy of visual estimated blood loss in postpartum haemorrhage by midwives and nurses, as well as exploring its influencing factors.BackgroundTimely recognition of postpartum haemorrhage is critical in saving maternal lives. Yet midwives and nurses can barely distinguish whether the blood loss has reached a life-threatening amount without precise measurement. Understanding their ability to accurately estimate the amount of blood loss and the influencing factors can help improve this ability with effective measures.DesignThis research was a multicenter cross-sectional survey with convenient sampling.Material and methodsUsing a modified online visual estimation questionnaire of blood loss, the QR code of this survey was sent to midwives and obstetrical nurses engaged in clinical practice in secondary and tertiary hospitals in Shanghai. A descriptive analysis was performed with demographics and the responses of visual estimated blood loss of each volume. The difference and consistency of the responses of each volume were evaluated. The relationship between each demographic characteristic and accuracy was explored. STROBE statement checklist was chosen for reporting the study process.ResultsA total of 361 midwives and nurses participated in the survey. The finding showed an overall accuracy of 30.52% (1763/5776), with 25.3% and 18.0% subjects distinguishing postpartum haemorrhage (500 ml) and severe postpartum haemorrhage (1000 ml), respectively. The Kappa coefficients were slight to moderate (0.037-0.590). There were no differences among the categories of gender, age, academic degree, position, title, working experience in years, working department and reported methods of blood loss estimation with regard to accuracy. However, having institutional guidance for blood loss calculation showed a significant relationship with higher accuracy.Relevance to clinical practiceWhile representing a relatively well-developed area in China, the accuracy of visual estimated blood loss was not satisfactory, as suggested in other developed countries around the world. Training and institutional guidance on blood loss quantification should be provided in midwifery settings, regardless of how the level of medical development is advanced.ConclusionsThe accuracy of VEBL was low even with a visual aid, especially when the volume exceeds 500 ml. To improve accuracy, institutions should make standardadized assessment guidance and provide regular training for blood loss quantification.

Project description:OBJECTIVE:We aimed to better understand how well postpartum blood loss and common postpartum hemorrhage (PPH) definitions (i.e. blood loss ?500ml = PPH, ?1000ml = "severe" PPH) correlate with postpartum anemia and fall in hemoglobin. METHODS:Secondary analysis of data from three randomized trials that objectively measured postpartum blood loss and pre- and post-delivery hemoglobin among vaginal deliveries: one trial included 1056 home-births in Pakistan and two multi-country hospital-based trials included 1279 women diagnosed with PPH. We calculated Spearman's correlation coefficients (rs) for blood loss with hemoglobin drop and postpartum hemoglobin, and we compared PPH blood loss markers (?500ml, ?1000ml) with large hemoglobin drops (?2 g/dL) and the threshold for moderate postpartum anemia (<10g/dL). RESULTS:In the Pakistan study and the multi-country trials, blood loss was weakly correlated with hemoglobin drop (Pakistan: rs = -0.220, multi-country trials: rs = -0.271) and postpartum hemoglobin (Pakistan: rs = -0.220, multi-country trials: rs = -0.316). In both the Pakistan and multi-country trials, hemoglobin drop ?2 g/dL occurred in less than half of women with 500-999 ml blood loss (55/175 [31%] and 302/725 [42%], respectively) and was more common among women who bled ?1000ml (19/28 [68%] and 347/554 [63%], respectively). Similarly, in the Pakistan and multi-country trials, postpartum anemia <10 g/dL was less frequent among women who bled 500-999 ml (55/175 [31%] and 390/725 [54%], respectively) and more frequent among women with ?1000ml blood loss (20/28 [71%] and 416/554 [75%], respectively). CONCLUSIONS:Postpartum morbidity as measured by hemoglobin markers was common for women with blood loss ?1000ml and relatively infrequent among women with blood loss 500-999ml. These findings reinforce the importance of severe PPH as the preferred outcome to be used in research. The weak correlation between blood loss and hemoglobin markers also suggests that this relationship is not straightforward and should be carefully interpreted.

Dataset Information

Distribution of postpartum blood loss: modeling, estimation and application to clinical trials.

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Distribution of postpartum blood loss: modeling, estimation and application to clinical trials.

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