How well do postpartum blood loss and common definitions of postpartum hemorrhage correlate with postpartum anemia and fall in hemoglobin?

Abstract

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.

Fig 1

Moving average* of change in pre- to post-delivery hemoglobin (Fig 1A) and postpartum hemoglobin (Fig 1B) by postpartum blood loss (ml) in the Pakistan PPH prevention study (N = 1058) and the multisite PPH treatment studies (N = 1283). *Data from the Pakistan prevention study are depicted in grey and data from the multisite treatment studies are depicted in black. The circles represent the moving average of change in hemoglobin or postpartum hemoglobin at each blood loss interval and the brackets represent the 95% confidence intervals (CIs) of the moving average. The moving average for each 100ml interval reflects the mean hemoglobin drop or mean postpartum hemoglobin measured within the interval and the preceding and subsequent 100 ml intervals. The number of women included in calculation of the moving average at each blood loss interval is indicated in the data table.