Chorioamnionitis is a serious, acute infection that occurs within the womb during pregnancy or labor. This condition involves the tissues surrounding the fetus and requires prompt recognition and medical management. Understanding the factors that lead to this infection and how frequently it occurs allows for informed discussions with healthcare providers during prenatal care and delivery.
Defining Chorioamnionitis
Chorioamnionitis is defined as an inflammation or infection of the fetal membranes and the amniotic fluid that surrounds the developing baby. The condition takes its name from the two layers of the amniotic sac: the chorion, which is the outer layer, and the amnion, the inner membrane.
The infection typically begins when bacteria, naturally present in the mother’s lower genital tract, ascend through the cervix into the uterine cavity. Once inside, these microorganisms can infect the amniotic fluid, the placenta, and the membranes themselves. Common culprits include bacteria such as Escherichia coli and Group B Streptococcus.
Prevalence and Timing of Infection
The prevalence of chorioamnionitis depends significantly on the timing of delivery, specifically whether it occurs at term or prematurely. Across all births, the infection is approximated to occur in about 4% of deliveries, though this figure masks substantial differences between patient groups.
In full-term pregnancies, the rate of clinical chorioamnionitis is lower, typically falling in the range of 2% to 4% of deliveries. This incidence drops even further in term pregnancies where the membranes remain intact. The infection is overwhelmingly more common in cases of premature birth and premature rupture of membranes (PROM).
When the membranes rupture prematurely, the incidence of chorioamnionitis increases sharply, ranging from 40% to 70% in women with preterm labor or preterm premature rupture of membranes (PPROM). This infection is a major factor driving preterm delivery, with the highest rates found in the most extremely preterm gestations. The infection most often presents during the intrapartum period, meaning it is diagnosed while the mother is in labor or just before delivery.
Key Risk Factors
Certain circumstances create a pathway for bacteria to ascend into the uterus, significantly increasing the likelihood of developing chorioamnionitis. One of the most important factors is the premature or prolonged rupture of the membranes. Once the protective barrier of the amniotic sac is compromised, the time elapsed until delivery directly correlates with a higher risk of infection.
The duration of labor is also a major contributing factor, as prolonged labor provides more opportunity for bacteria to move upward from the vagina. The number of vaginal examinations performed after the membranes have ruptured can increase the risk by introducing bacteria closer to the cervix and uterus. Internal monitoring devices, which are sometimes used to track the baby’s heart rate or uterine contractions, also create a potential route for infection.
Pre-existing maternal infections, such as those caused by Group B Streptococcus or sexually transmitted infections, can predispose a person to chorioamnionitis. Other factors, including being a first-time mother, having a low socioeconomic status, or using tobacco and alcohol, are also associated with an elevated risk of developing this intrauterine infection.
Treatment Protocols and Associated Outcomes
Immediate medical management is required once chorioamnionitis is suspected or diagnosed to prevent severe outcomes for both the mother and the baby. The standard protocol centers on the prompt administration of broad-spectrum intravenous antibiotics. A common regimen involves a combination of medications like ampicillin and gentamicin, which target the likely bacterial culprits.
In addition to antibiotics, the definitive treatment is usually expedited delivery, regardless of the gestational age of the fetus. While the route of delivery is ideally vaginal, the infection increases the risk of needing a Cesarean delivery. The time between diagnosis and delivery does not typically impact the majority of adverse outcomes, allowing clinicians to prioritize a safe delivery method.
For the mother, potential complications include maternal sepsis, which is a life-threatening bloodstream infection, and postpartum hemorrhage. There is also an increased chance of developing endometritis, which is an infection of the lining of the uterus, especially after a Cesarean section. For the neonate, exposure to the infection significantly increases the risk of developing early-onset neonatal sepsis, pneumonia, and meningitis. In the long term, the infection has been associated with more serious complications for the baby, including chronic lung disease and cerebral palsy.