The Use of Hemoglobin and Hematocrit Values to Estimate Intrapartum Blood Loss

INTRODUCTION: The purpose of this study was to systematically review formulae using hemoglobin (Hb) or hematocrit (Hct) that have been derived, validated or used to objectively estimate intrapartum blood loss and determine their diagnostic accuracy. METHODS: MEDLINE, EMBASE, and Web of Science were searched from inception until 29 July 2016 for studies describing the use of Hb or Hct to estimate intrapartum blood loss in pregnant women. Studies were limited to humans, with no other search restrictions. Citation tracking and grey literature searches were performed. Two independent investigators screened titles and abstracts; performed data extraction; and completed risk of bias assessments using a revised tool for quality assessment of diagnostic accuracy studies (QUADAS-2). Disagreement was resolved through discussion or adjudication with a third reviewer. The study protocol was registered with the PROSPERO International Prospective Register of Systematic Reviews (CRD42016043505). RESULTS: Of the 6463 identified titles, 63 full-texts were retrieved and 13 studies included in qualitative synthesis. The risk of bias was deemed to be low in five and unclear in eight studies. A total of 12 unique formulae were identified that used Hb or Hct as variables (in addition to height and bodyweight) to estimate peripartum blood loss, of which two were derived and seven were validated. Meta-analysis was not possible due to clinical and methodological heterogeneity between studies. CONCLUSION: This systematic review identified 12 formulae that could provide an objective method for estimating intrapartum blood loss. These formulae need to be validated by adequately powered, prospective studies.