Suspected Chorioamnionitis and Myometrial Contractility: Mechanisms for Increased Risk of Cesarean Delivery and Postpartum Hemorrhage

Objective: Chorioamnionitis is associated with an increased risk of cesarean delivery and uterine atony. We hypothesized that the onset of maternal fever is temporally associated with decreased uterine contractility. Study Design: Retrospective cohort. Setting: Academic center. Patients: Term participants who developed a fever in the setting of an intrauterine pressure catheter. Main Outcome Measure: Montevideo units (MVUs) and oxytocin dose at time 0 (first oral temperature ≥38°C) and in the five 1--hour blocks preceding and following T0. Analysis: Montevideo units relative to the onset of fever. Results were adjusted for oxytocin dose and parity in a mixed-effects model. Results: One hundred participants were included. Uterine contractility was maintained for 2 hours after the onset of maternal fever but thereafter significantly and steadily declined by an average of 6.9 ± 3.2 MVU/h (P =.03), despite the absence of a parallel decline in oxytocin exposure. Multiparas and nulliparas showed a similar pattern of waning uterine contractility. Patients who delivered vaginally maintained contractility, while those who delivered via cesarean had diminishing contractility (P =.01). The postpartum hemorrhage (PPH) rate (postpartum bleeding requiring treatment) was 32%. Conclusions: A decline in myometrial contractility occurs 2 hours following the onset of maternal fever. Increased risk of cesarean delivery appears to be directly associated with waning uterine contractility and decreased uterine responsiveness to oxytocin. Clinically, close attention should be given to maintaining adequate uterine contractions following a diagnosis of suspected chorioamnionitis. The likelihood of successful vaginal delivery may decrease over time, and the risk of PPH is clinically significant.