Evidence of placental abruption as a chronic process: Associations with vaginal bleeding early in pregnancy and placental lesions

Background: Clinicians widely regard placental abruption as an acute event, though accumulating data point towards abruption being the end-result of chronic processes early in pregnancy, and perhaps even extending to conception. The Collaborative Perinatal Project was a prospective cohort study performed from 1959 to 1966 in the United States. Since enrolled pregnancies were managed without the biases created by modern perinatal surveillance and interventions, the natural history of disease in these data is ideal to study obstetrical complications such as placental abruption. Objective: We assessed the associations versus contributions of the clinical feature of early gestational vaginal bleeding and histologic lesions (chronic and acute) with placental abruption. Study design: Women enrolled in the Collaborative Perinatal Project (1959-1966) were used, restricting the analysis to those that delivered singleton births (n = 46,364). Risks of placental abruption were compared between women with and without vaginal bleeding at <20 weeks gestation. We also examined the relationships between placental abruption and chronic and acute histologic lesions, including infarcts, decidual necrosis, presence of macrophages in the decidua, amnion or chorion, and neutrophil infiltration in the amnion, chorion, placental surface, and umbilical vein. Results: Any episode of vaginal bleeding at <20 weeks in pregnancy conferred an increased risk of placental abruption (adjusted relative risk (RR) 1.6, 95% confidence interval (CI) 1.3, 1.8). The greatest risk occurred with bleeding in both the first two trimesters (RR 3.1, 95% CI 2.3, 4.1). The presence of histologic lesions in the placenta, cord and membranes similarly carried an increased risk of placental abruption, even in the absence of vaginal bleeding. The risk of abruption was, however, highest in the presence of both histologic lesions and vaginal bleeding early in pregnancy. Conclusion: Vaginal bleeding early in pregnancy and histologic lesions of the placenta, umbilical cord, and membranes are associated with increased risk of placental abruption in later pregnancy. However, the increased risk associated with placental lesions, especially chronic inflammatory lesions, even in the absence of early vaginal bleeding, suggests that prolonged inflammation may be implicated in placental abruption.