Postpartum hemorrhage in a large prospective cohort study: is uterine atony really the main culprit?

BackgroundUterine atony ([~]70%), lacerations ([~]20%) and placenta-related problems ([~]10%) are assumed main reasons for postpartum hemorrhage genesis. Coagulation components predictive for postpartum blood loss can be identified prepartum and before traditionally assumed main reasons are observed. ObjectivesTo better understand postpartum hemorrhage genesis, we prospectively researched prepartum clinical information, presence of assumed main reasons and peripartum coagulation changes in parturient women. Study designIn 676 women with vaginal deliveries, age, BMI, parity, gestation age, duration of second stage of labor and presence and type of assumed main reasons (uterine atony, lacerations and placenta-related problems) were recorded. Measured blood loss within 24h postpartum defined no, non-severe or severe PPH (<500ml, [&ge;]500ml to <1000ml, [&ge;]1000ml). Hemoglobin, platelet count, fibrinogen, factor II and factor XIII activity were measured at admission and 24-48h postpartum. ResultsOf 191 women developing postpartum hemorrhage, 53.9% did not show assumed main reasons (expected <5%, p<.001). Of 45 women with severe postpartum hemorrhage, 15.5% were without assumed main reasons (<5%, p<.001). Sole atony occurred less frequently than expected (8.2% in non-severe and 35.5% in severe PPH, p<.001). FXIII showed the largest decrease of coagulation factors by far, from no (-12%) to non-severe (-20%) and severe postpartum hemorrhage (-32%, p<.001). Duration of the second stage of labor was longer in women developing postpartum hemorrhage later on (71 vs. 46 minutes, p=.004), but was not different between women with or without assumed main reasons. ConclusionUterine atony frequency is low in non-severe postpartum hemorrhage, but progresses from non-severe to severe postpartum hemorrhage. It can thus not be the frequent reason for postpartum hemorrhage it is assumed to be, as all postpartum hemorrhages start as non-severe. A prolonged second stage of labor together with an ongoing (likely self-reinforcing) consumptive coagulopathy helps to explain postpartum hemorrhage genesis. FXIII is a prepartum predictor of postpartum blood loss and shows the most pronounced peripartum coagulation factor loss in any setting. This might allow to identify new treatment pathways.