Insights in the (patho)physiology of uterine activity in the first 30 minutes after childbirth

The incidence of postpartum hemorrhage (PPH) has increased despite consistent use of prophylactic treatment. To date, little is known about postpartum uterine activity. This study investigates the association between various uterine activity parameters and blood loss in the first 30 minutes postpartum. Term pregnant patients who received postpartum continuous electrophysiological uterine monitoring were included. Postpartum blood loss was measured using weighting. From a 30-min electrohysterography-derived tocogram, a computer-based algorithm was used to extract uterine activity parameters. These included total area under the curve (AUC), AUC from baseline, maximum amplitude and baseline tone. Scatterplots between various UA parameters and logarithmically transformed total blood loss were made and Pearson correlation coefficients were calculated. UA-parameters were compared between non-PPH patients and patients with PPH, including the different PPH etiologies. 119 patients were included of which 24 had PPH (blood loss ≥ 500 mL). Total blood loss showed no significant association with the various UA-parameters. Patients with PPH due to a retained placenta (n=6) showed significantly higher total UA-AUC (5.5 vs 5.2, p=0.007), UA-AUC from baseline (5.4 vs 5.1, p=0.003) and maximum amplitude (3.0 vs 2.9, p=0.024) compared to patients without PPH. Increased postpartum uterine activity may reflect compensatory but ineffective myometrial activation in patients with PPH due to a retained placenta. Due to the limited sample size and exploratory nature of the analyses, these results should be interpreted with caution. • Better insight into postpartum uterine (patho)physiology may improve care • Electrohysterography enables continuous monitoring of uterine activity after birth • Uterine activity is compared between non-PPH and various PPH etiologies • Uterine activity increases in patients with PPH due to a retained placenta