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Intra–Amniotic Infection


by Antonette T. Dulay, MD

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 and neonate. Symptoms include fever, uterine tenderness, foul-smelling vaginal discharge, and maternal and fetal tachycardia. Diagnosis is by specific clinical 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)

  • Multiple digital examinations during labor in women with ruptured membranes

  • Long labor

  • Preterm premature rupture of membranes


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

  • Neonatal 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 and/or vaginal discharge. However, infection may not cause typical symptoms (ie, subclinical infection).


  • 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 or vaginal discharge

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, ephedrine); 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

  • Positive culture

  • 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.


  • Broad-spectrum antibiotics plus delivery

Treatment is broad-spectrum IV antibiotics plus delivery. A typical intrapartum antibiotic regimen is ampicillin 2 g IV q 6 h plus gentamicin 1.5 mg/kg IV q 8 h. How long antibiotics are given varies, depending on individual circumstances (eg, how high the fever was, when the fever last spiked in relation to delivery). 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 women with preterm PROM (see Premature Rupture of Membranes (PROM)). Broad-spectrum antibiotics are also given to women with preterm PROM to prolong latency until delivery and decrease risk of infant morbidity and mortality.

Key Points

  • Intra-amniotic infection can be subclinical and relatively asymptomatic.

  • Consider the diagnosis when fetal or maternal tachycardia or refractory preterm labor is present, as well as when women have the more classic symptoms of infection (eg, fever, discharge, pain, tenderness).

  • Consider analyzing and culturing amniotic fluid if women have refractory preterm labor or preterm PROM.

  • Treat intra-amniotic infection with broad-spectrum antibiotics plus delivery.

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