Infections are increasingly recognized as important contributors of maternal, fetal, and neonatal complications. Although the exact incidence of infections complicating labor is difficult to ascertain, available data suggest that it varies from 1 to 4 percent of all births and up to 60 percent of preterm births. These can generally be divided into two major categories, ascending genital tract infections and hematogenously spread infections from the mother. The symptoms associated with infections during labor can vary significantly, and it is not infrequent for some of these entities to be subclinical. As such, a high index of suspicion is required, along with appropriate knowledge of preventive and therapeutic approaches. Diagnostic tools include serologic testing; culture of blood, amniotic fluid, placenta, and membranes; pathologic examination of the placenta; and umbilical cord and molecular approaches.
Ascending genital tract infections are usually bacterial and almost always polymicrobial. These can occur in the context of intact or ruptured membranes and can be either subclinical or present as full-blown chorioamnionitis with maternal and fetal symptoms.
Chorioamnionitis is an infection of the chorion and amnion, which can progress to involve the umbilical cord, placenta, and fetus itself. It is characterized by the infiltration of these membranes by neutrophil polymorphs, which starts at the interface between the decidua and chorion at the level of the os. The most common microorganisms involved include Ureaplasma spp., Mycoplasma spp., enterococci, streptococci, coliforms, and staphylococci.
Intrapartum risk factors for the development of chorioamnionitis include multiple examinations during labor, prolonged labor, nulliparity, bacterial vaginosis or group B streptococcal (GBS) colonization, meconium, use of internal monitoring, and epidural anesthesia. Finally, alcohol use and cigarette smoking are predisposing factors.
Frequently associated with preterm prelabor rupture of the membranes (PPROM) and preterm labor (PTL), chorioamnionitis is often suspected as playing a causative role in these pathologies. Ascension of microorganisms via the genital tract to the membranes results in the production and release of proinflammatory cytokines and chemokines, which in turn may weaken the membranes and lead to PPROM. In addition, the release of prostaglandins associated with the process of inflammation may induce cervical changes and result in preterm delivery. The incidence of microbial invasion of amniotic cavity (MIAC) is as high as 30 percent in women with PPROM. Up to 34 percent of women with term PROM and 13 percent of women with an episode of PTL have been shown to have MIAC. The role of inflammation in the cascade of intraamniotic infection is extremely important. A recent study of 224 women with PPROM who underwent amniocentesis revealed a proven intraamniotic infection in 23 percent and a rate of intraamniotic inflammation of 42 percent. Infectious agents most commonly isolated included Ureaplasma urealyticum (38 samples), Candida spp. (five samples), and Escherichia coli (two samples). These data clearly demonstrated that inflammation of the amniotic cavity, independent of ...