Background: Chorioamnionitis complicates up to 4 percent of pregnancies and is a major contributor to maternal and neonatal mor-bidity. Established risk factors for chorioamnionitis include prolonged labor and frequent vaginal examinations during labor, suggesting that external contamination during childbirth is a key etiologic factor in this infection. In addition, some evidence suggests that some mothers may be at higher risk of chorioamnionitis because of vaginal colonization with virulent bacteria, especially group B streptococci or Ureaplasma urealyticum. Newer evidence points to a contribution from altered inflammatory response in some mothers.

Carrying a tumor necrosis factor α allele (i.e., TNF-α₂) is associated with a three-fold risk of clinical chorioamnionitis. Other genetically determined influences on the immune response also may be associated with the infection. If immune response is a significant factor in the etiology of chorioamnionitis, some mothers could be at risk of recurrent infection in subsequent pregnancies. Laibl and colleagues examined data from a large university labor and delivery service to establish the risk of recurrent chorioamnionitis in subsequent pregnancies.

The Study: The researchers studied records of more than 23,000 women who delivered their first and second babies at a hospital in Texas between January 1988 and May 2005. The women were nulliparous on entry to the study, and the first delivery was required to be a singleton vaginal birth. Mothers with human immunodeficiency virus infection were excluded from the study. Those with hypertension and diabetes also were excluded because of the high rates of labor induction associated with these diseases.

Data collected on each study participant included information on epidural anesthesia, induction of labor, use of internal fetal monitors, duration of total labor and second stage of labor, duration of ruptured membranes, and history of premature rupture of membranes (PROM). The diagnosis of chorioamnionitis was based on clinical criteria of a temperature elevated to 100.4° F (38° C) or higher, plus signs such as fetal or maternal tachycardia, uterine tenderness, or malodorous vaginal discharge. Patients with chorioamnionitis in the initial pregnancy were compared with those without it.

Results: Of the 23,397 women in the study, 10 percent developed chorioamnionitis during their first pregnancy. Women with chorioamnionitis were significantly different from those without it, including being older (average age of 21 versus 20 years), having longer labors, and having heavier babies (average birth weight of 3,355 g [7 lb, 6oz] compared with 3,180 g [7 lb]). They also were significantly more likely to have induced or augmented labors, use epidural anesthesia, have a prolonged second stage of labor, and be monitored with internal devices.

Six percent of mothers who had chorioamnionitis with the initial delivery also developed the condition during the subsequent delivery, compared with only 2 percent of mothers who did not have chorioamnionitis with the initial birth. Women who had recurrent chorioamnionitis differed significantly from those who had the condition only in the index pregnancy, including in duration of labor, induction or augmentation of labor, length of second stage of labor, duration of ruptured membranes, use of internal monitors, and rate of cesarean delivery. After adjusting for ethnicity, age, rupture of membranes longer than 24 hours, PROM, duration of labor, gestational age at delivery, augmentation or induction of labor, use of internal monitors, and epidural anesthesia, the risk of chorioamnionitis in the second delivery was significantly associated with a previous episode.

Conclusion: The authors conclude that women with a previous episode of chorioamnionitis have at least a twofold risk of recurrence. This risk is independent of other factors associated with chorioamnionitis and could indicate an inherent maternal predisposition to the infection.