The key clinical findings associated with clinical chorioamnionitis include fever, uterine fundal tenderness, maternal tachycardia (>100/min), fetal tachycardia (>160/min) and purulent or foul amniotic fluid [2
Maternal fever is the most important clinical sign of chorioamnionitis. Temperature > 100.4°F is considered abnormal in pregnancy. While isolated low-grade fever (<101°F) may be transient in labor, fever >100.4°F persisting more than 1h or any fever ≥101°F warrants evaluation and appropriate intervention. Fever is present in 95–100% of cases of clinical chorioamnionitis and typically is required for the diagnosis (see below). Fever in the setting of epidural anesthesia, particularly among nulliparous women with prolonged labor (so called epidural fever) is often encountered and poses a diagnostic quagmire vis-à-vis chorioamnionitis [23
]. This is because i) in addition to fever, the two conditions share other major risk factors (low parity and prolonged labor), ii) epidural anesthesia masks signs of chorioamnionitis such as fundal tenderness, and iii) medications given during epidural anesthesia may induce maternal or fetal tachycardia and therefore confound the diagnosis of chorioamnionitis [24
]. The exact mechanism of epidural fever is unknown, but it is thought to be the result of epidural sympathetic blockade of thermoregulatory processes such as sweating [24
]. In one study, maternal fever was more common among the epidural group when placental inflammation was present (35% vs. 17%) but not in the absence of inflammation (11% vs. 9%). This suggests that the pathologic basis for epidural fever is chorioamnionitis [23
]. In sum, the concept of epidural fever remains controversial and warrants additional studies.
Maternal tachycardia (>100 BPM) and fetal tachycardia (>160 BPM) occur frequently in chorioamnionitis, being reported in 50–80% and 40–70% of cases respectively. Tachycardia may be present in the absence of chorioamnionitis and requires careful assessment for alternative etiologies. Medications such as ephedrine, antihistamines, and beta agonists may raise maternal or fetal heart rate. However, the combination of maternal fever and maternal and/or fetal tachycardia are strongly suggestive of intrauterine infection and should be treated accordingly.
Aside from the objective measurements of maternal fever and tachycardia, other signs of chorioamnionitis are highly subjective. Uterine fundal tenderness and a foul odor to the amniotic fluid are reported in only 4–25% of cases of chorioamnionitis [4
]. Fundal tenderness is difficult to interpret in the context of the pain of labor and may be masked by analgesics including epidural or confounded by the pain associated with placental abruption. Purulence or foul odor of amniotic fluid are more likely to be present with severe or prolonged infection and may be organism-specific, but in any case may or may not be appreciated by clinicians.
Chorioamnionitis that is subclinical by definition does not present the above clinical signs but may manifest as preterm labor or, even more commonly, as preterm premature rupture of membranes (PPROM). In addition, premature ROM at term (membrane rupture at ≥37 weeks gestation but prior to onset of uterine contractions), which occurs in 8% or less of term births, is associated with an increased risk of chorioamnionitis [25