How are intra-amniotic infections (IAIs) diagnosed in women with preterm labor?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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Tocolytics are contraindicated in the presence of symptomatic IAI. The definition of IAI infection (ie, chorioamnionitis) includes a temperature greater than 38.0°C (100.0°F) and 2 of the 5 following signs:

  • WBC count greater than 15,000 cells/mm3

  • Maternal tachycardia greater than 100 beats per minute (bpm)

  • Fetal tachycardia greater than 160 bpm

  • Tender uterus

  • Foul-smelling discharge

In situations in which the diagnosis remains unclear, an amniocentesis for fluid culture (aerobic/anaerobic bacteria), Gram stain (bacteria present if Gram stain is positive or if WBC count is >50 cells/mm3), glucose level (positive if < 15 mg/dL), or leukocyte esterase evaluation may be considered. However, amniocentesis may result in a false-positive FFN test result if the FFN is performed after amniocentesis. [2]

A study by Romero et al indicated that IAI can be quickly and accurately diagnosed with polymerase chain reaction assay with electrospray ionization time-of-flight mass spectrometry (PCR/ESI-MS). In the study, amniotic fluid from 142 women with preterm labor with intact membranes underwent culturing and PCR/ESI-MS testing. Standard culturing techniques detected microbial invasion of the amniotic cavity in 7% of these patients, while PCR/ESI-MS detected it in 12% of them. Compared with women in whom both tests were negative, those patients who had negative cultures but positive PCR/ESI-MS results had a significantly greater incidence of intra-amniotic inflammation and acute histologic chorioamnionitis, as well as a shorter time to delivery and offspring with a greater perinatal mortality risk. [25]

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