Which bacterial pathogens are most common in stillbirth?

©tolikoff2013 - stock.adobe.com

Research published in Obstetrics & Gynecology aimed to better characterize stillbirth related to infection using clinical, histologic, and microbiologic data. According to the authors, approximately 10% to 20% of stillbirths are reported to be caused by infection in high-income countries, but the number is likely much higher in low-income countries.

Methods
The secondary analysis examined 512 stillbirths from a prospective, multisite, geographically and racially/ethnically diverse population-based study conducted by the Stillbirth Collaborative Research Network of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Cases underwent evaluation that included maternal interview, chart abstraction, biospecimen collection, fetal autopsy, and placental pathology. Each stillbirth was assigned a cause of death using an algorithm developed by the Stillbirth Collaborative Research Network investigators (INCODE). Conditions were considered to be “probable” or “possible” causes of stillbirth, or present but unlikely to be contributors to the stillbirth.

Findings
In the initial analysis of causes of death among the 512 stillbirths, infection was determined to be a probable or possible cause in 66 (12.9%). Of these, 65% were antepartum and 35% were intrapartum stillbirths. Infection accounted for a higher proportion of stillbirths relatively early in gestation, particularly before 23 weeks of gestation, and were associated with a higher percentage of stillbirths in non-Hispanic black women compared with non-Hispanic white women or Hispanic women. 

Of the 66 cases of stillbirth caused by infection, 36% (95% CI 35-38%) were categorized as infection being the probable cause of death and 64% (95% CI 62-65%) were categorized as possible cause of death. Fetal bacterial culture results were available in 47 (71%) cases. Thirty-five of these cases grew identifiable organisms. The most prominent species were Escherichia coli (19% probable, 29% possible), group B streptococcus (GBS) (8% probable, 12% possible), and enterococcus species (8% probable, 12% possible).

From placental pathology, the authors were able to reveal chorioamnionitis in 50 (76%), funisitis in 27 (41%), villitis in 11 (17%), deciduitis in 35 (53%), necrosis in 27 (41%) and viral staining in seven (11%) cases. In infection-related stillbirth cases, the likely causative non-bacterial organisms identified were parvovirus in two (3%) cases, syphilis in one (2%) case, cytomegalovirus (CMV) in five (8%) cases, and herpes in one (2%) case.

Conclusions
Based on their findings that the most common bacterial pathogens in cases of stillbirth were E coli GBS, and enterococcus species, the authors suggest prevention efforts should target these organisms. Because stillbirth due to infection shared pathophysiology with spontaneous preterm birth (sPTB), efforts to reduce infections may also reduce sPTB as well as stillbirths.