Incidence and risk factors for postpartum infections: A Norwegian cohort study, 2012-2020

Few epidemiological studies have examined postpartum infections in the Nordic countries. This study aimed to assess the incidence and risk factors for postpartum infections in Norway.

We conducted a historical cohort study including all deliveries in Norway from 2012 to 2020, using linked nationwide data from the Medical Birth Registry of Norway, the Norwegian Patient Registry, and Statistics Norway. We defined two outcomes: endometritis/puerperal sepsis (O85, International Classification of Diseases 10th version (ICD-10); the code does not differentiate between endometritis and puerperal sepsis, and endometritis predominates) and other postpartum infections (O86, ICD-10). Associations were estimated as relative risks (RR) with 95% confidence intervals (CI) using log-binomial regression.

Among 516 874 deliveries, we identified 5942 cases (1.15%) of endometritis/puerperal sepsis (O85) and 8833 (1.71%) of other postpartum infections (O86). The incidence of endometritis/puerperal sepsis increased over time from 0.93% in 2012 to 1.38% in 2020 (test for trend, p < 0.001). After adjusting for all covariates, delivery-related factors demonstrated the strongest associations with both outcomes, especially emergency cesarean section (aRR_O85 2.8; 95% CI 2.6-3.0/aRR_O86 5.1; 95% CI 4.8-5.5) and postpartum hemorrhage (aRR_O85 3.2; 2.9-3.4/aRR_O86 2.0; 1.9-2.2). Risk factors not directly related to delivery, such as multifetal gestation, obesity, nulliparity and maternal single status, were also associated with both outcomes (aRRs in the range of 1.2-2.5). Chorioamnionitis lies on the same infectious continuum as postpartum endometritis and is treated with intrapartum antibiotics, usually discontinued after delivery unless persisting signs of infection. We found a strong association between chorioamnionitis/intrapartum infection and postpartum infections (aRR_O85 5.7; 5.1-6.4/aRR_O86 3.2; 2.9-3.6). Alongside the strong associations with postpartum infections, we also observed an increasing incidence over time in chorioamnionitis/intrapartum infection (p < 0.001) and postpartum hemorrhage (p < 0.001).

Postpartum infections are common, and the incidence of endometritis/puerperal sepsis is increasing. For all postpartum infections, delivery-related factors demonstrate the strongest associations. Postpartum hemorrhage and chorioamnionitis/intrapartum infection may represent key targets for prevention/prevention of progression. Revision of the coding system is necessary to enable differentiation between puerperal sepsis and endometritis for better surveillance.