Changes between pre- and postpartum hemoglobin might be useful for optimizing the postpartum diagnosis of postpartum hemorrhage (PPH), defined as a blood loss exceeding 500 mL. This study's principal objective was to estimate the mean change in hemoglobin (between pre/post-delivery hemoglobin) among women with vaginal deliveries and PPH. The secondary objectives were to analyze: hemoglobin changes according to blood volume loss, the appropriateness of standard thresholds for assessing hemoglobin loss, and the intrinsic and extrinsic performances of these threshold values for identifying PPH. French maternity units (n = 182) participated in the prospective HERA cohort study. Women with a vaginal delivery at or after a gestation of 22 weeks with a PPH (n = 2964) were eligible. The principal outcome was hemoglobin loss in g/L. The mean hemoglobin change was 30 ± 14 g/L among women with a PPH. Overall, hemoglobin decreased by at least 10% in 90.4% of women with PPH. Decreases ≥ 20 g/L and ≥40 g/L were found, respectively, in 73.9% and 23.7% of cases. Sensitivity and specificity values for identifying PPH were always <65%, the positive predictive values were between 35% and 94%, and the negative predictive values were between 14% and 84%. Hemoglobin decrease from before to after delivery should not be used as a PPH diagnostic screening test for PPH diagnosis for all vaginal deliveries.
Keywords: blood loss estimation; hemoglobin change; postpartum hemorrhage; screening test; vaginal delivery.