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Intra-amniotic infection (formerly called chorioamnionitis) is infection of the chorion, amnion, amniotic fluid, placenta, or a combination. Infection increases risk of obstetric complications and problems in the fetus. Symptoms include fever, uterine tenderness, foul-smelling vaginal discharge, and maternal and fetal tachycardia. Diagnosis is by specific criteria or, for subclinical infection, analysis of amniotic fluid. Treatment includes broad-spectrum antibiotics and delivery.

Intra-amniotic infection typically results from an infection that ascends through the genital tract.

Risk factors: Risk factors include the following:

• Preterm labor
• Nulliparity
• Meconium-stained amniotic fluid
• Internal fetal or uterine monitoring
• Presence of genital tract pathogens (eg, those that cause sexually transmitted diseases or bacterial vaginosis, group B streptococci)
• Digital examinations during labor in women with ruptured membranes
• Long labor
• Preterm premature rupture of membranes

Complications: Intra-amniotic infection can cause as well as result from preterm premature rupture of membranes or preterm delivery. This infection accounts for 50% of deliveries before 30 wk gestation. It occurs in 33% of women who have preterm labor with intact membranes, 40% who have premature rupture of membranes (PROM) and are having contractions when admitted, and 75% who go into labor after admission for PROM.

Fetal complications include increased risk of the following:

• Preterm delivery
• Apgar score < 3
• Infection (eg, sepsis, pneumonia, meningitis)
• Seizures
• Cerebral palsy
• Death

Maternal complications include increased risk of the following:

• Bacteremia
• Need for cesarean delivery
• Uterine atony
• Postpartum hemorrhage
• Pelvic abscess
• Thromboembolism
• Wound complications

Septic shock, coagulopathy, and adult respiratory distress syndrome are also risks but are uncommon if infection is treated.

Symptoms and Signs

Intra-amniotic infection typically causes fever. Other findings can include maternal tachycardia, fetal tachycardia, uterine tenderness, and foul-smelling amniotic fluid. However, infection may not cause typical symptoms (ie, subclinical infection).

Diagnosis

• Clinical criteria
• Amniocentesis for suspected subclinical infection

Diagnosis usually requires a maternal temperature of > 38° C (> 100.4° F) plus ≥ 2 of the following:

• Maternal WBC count > 15,000 cells/μL
• Maternal tachycardia (heart rate > 100 beats/min)
• Fetal tachycardia (heart rate > 160 beats/min)
• Uterine tenderness
• Foul-smelling amniotic fluid

Presence of a single symptom or sign, which may have other causes, is less reliable. For example, uterine pain and tenderness may result from abruptio placentae. Maternal tachycardia may be due to pain, epidural anesthesia, or drugs (eg, ephedrineSome Trade Names
PRETZ-D
Click for Drug Monograph
); fetal tachycardia may be due to maternal use of drugs or fetal hypoxemia. Maternal and fetal heart rates also increase during fever. However, if intra-amniotic infection is absent, heart rates return to baseline as these conditions resolve. If fetal or maternal tachycardia is disproportionate to or occurs without such conditions or if it persists despite resolution of these conditions, intra-amniotic infection is suspected.

Subclinical infection: Refractory preterm labor (persisting despite tocolysis) may suggest subclinical infection. If membranes rupture prematurely before term, clinicians should also consider subclinical infection so that they can determine whether induction of labor is indicated.

Amniocentesis with culture of amniotic fluid is the best way to diagnose subclinical infection. The following fluid findings suggest infection:

• Presence of any bacteria or leukocytes using Gram staining
• Glucose level < 15 mg/dL
• WBC count > 30 cells/μL
• Leukocyte esterase level at trace or higher levels

Other diagnostic tests for subclinical infection are under study.

Treatment

• Broad-spectrum antibiotics

Treatment is broad-spectrum IV antibiotics plus delivery. A typical antibiotic regimen is ampicillinSome Trade Names
OMNIPEN
PRINCIPEN
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2 g IV q 6 h plus gentamicinSome Trade Names
GARAMYCIN
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1.5 mg/kg IV q 8 h. The antibiotics reduce risk of morbidity due to infection for mother and neonate.

Risk of intra-amniotic infection is decreased by avoiding or minimizing digital pelvic examinations in patients with preterm PROM (see Abnormalities and Complications of Labor and Delivery: Premature Rupture of Membranes (PROM)).

Last full review/revision February 2010 by Antonette T. Dulay, MD

Content last modified February 2010