Chorio-amnionitis
Strictly defined, chorio-amnionitis is an infection of the amniotic cavity, fetal membranes, placenta, and/or decidua. Other terms used to describe this condition are intra-amniotic infection, amnionitis, and amniotic fluid infection. This is usually a polymicrobial infection involving organisms commonly found in the vagina. Research studies indicate that chorio-amnionitis complicates 0.5–10% of all pregnancies. A distinction between histologic chorio-amnionitis and clinical amnionitis is often made. The former is defined by infiltration of the fetal membranes with polymorphonuclear leukocytes. It occurs more often than clinical chorio-amnionitis, and usually is discovered in cases in which there are no clinical signs or symptoms of infection as discussed below. Up to 20% of term deliveries and nearly half of preterm deliveries are associated with histologic chorio-amnionitis. Clinical chorio-amnionitis is seen in 1–2% of term and 5–10% of preterm births. Despite continued advances in antibiotic therapy, intra-amniotic infection is associated with increased maternal and neonatal morbidity and mortality.
Etiology
While the majority of cases of chorio-amnionitis are due to an ascending infection from the vagina and cervix, intra-amniotic infection may also occur via the hematogenous route or after invasive procedures such as amniocentesis, chorionic villous sampling or cerclage. Any factor that increases the risk of prolonged exposure of the fetal membranes and/or uterine cavity to ascending bacteria from the vagina will increase the risk of chorio-amnionitis. Such factors include prolonged rupture of membranes, frequent vaginal examinations, prolonged labor, premature labor, nulliparity, internal fetal monitoring, and meconium-stained amniotic fluid.
Clinical features
The diagnosis of chorio-amnionitis is based on observation of the following reactions of the patient and her fetus to an intra-amniotic infection.
- Maternal temperature greater than 100.4ºF or 38ºC in the absence of any obvious causes of fever
- Maternal tachycardia
- Uterine tenderness
- Malodorous or purulent amniotic fluid
- Elevated white blood cell count (>15,000 mL)
- Fetal tachycardia
- Fetal heart rate pattern with decreased variability and/or decelerations
In situations in which the diagnosis is unclear, the gold standard is a positive amniotic fluid culture and gram stain obtained via amniocentesis. It is not essential for an amniocentesis to be performed in all cases in which chorio-amnionitis is suspected. Most often, the diagnosis is made on the basis of the clinical observations noted above. Amniocentesis should be considered in those patients in preterm labor without obvious signs of intra-amniotic infection who fail to respond to tocolysis with a single agent or in those patients who have recurrent preterm labor. The presence of low amniotic fluid glucose levels (<15 mg/dL) or elevated cytokines (interleukin-1, interleukin-6, and tumor necrosis factor) has been associated with the histologic diagnosis of chorio-amnionitis. Unfortunately, testing amniotic fluid for the presence of cytokines is not routinely available. Testing maternal blood for elevated C-reactive protein provides little if any diagnostic information.
Perinatal complications
The risk of fetal infection associated with chorio-amnionitis is 10–20%. Potential infectious morbidities include pneumonia, meningitis, and sepsis. In addition, greater evidence is accumulating to implicate the role of intra-amniotic infection in neurodevelopmental delay and cerebral palsy. These complications are more severe in premature infants. While the exact etiology of neurodevelopmental delay and cerebral palsy in infants born to mothers with chorio-amnionitis is not known with certainty, the leading theory suggests that it is due to an elevation in fetal cytokine levels as part of the fetal inflammatory response syndrome. The elevation in cytokines has been associated with destruction of the white matter within the brain (cystic periventricular leukomalacia) and the development of neurologic delay or cerebral palsy. Lastly, chorio-amnionitis can lead to fetal or neonatal death.
Maternal complications
While not as common as fetal and neonatal complications, chorio-amnionitis may result in significant maternal morbidity ranging from pelvic infection to septic shock. With continuing advances in medical care, maternal mortality due to chorio-amnionitis is exceedingly rare. In fact, in four relatively recent studies involving more than 700 women with chorio-amnionitis, no maternal deaths were reported.
Management
After a diagnosis of chorio-amnionitis is made, parenteral antibiotics should be started followed by delivery regardless of gestational age. Antipyretic therapy with acetaminophen and/or cooling blankets help to decrease febrile morbidity. Since many different organisms have been associated with intra-amniotic infection (Box 13.1), most authorities recommend combination antibiotics or single-agent broad-spectrum antibiotics. Many different regimens have been proposed but ampicillin given along with an aminoglycoside such as gentamicin has proven to be safe and effective. In cases in which anaerobic organisms are suspected or recovered, an antimicrobial with anaerobic coverage such as clindamycin or metronidazole is recommended. Similarly, either clindamycin or metronidazole should be added if cesarean section is performed.
Box 13.1 Organisms commonly associated with chorio-amnionitis
Aerobic
Gram negative
Escherichia coli
Other gram-negative bacilli
Gram positive
Streptococcus agalactiae
Enterococcus faecalis
Staphylococcus aureus
Streptococcus species
Anaerobic
Gram negative
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