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Objectives This study was conducted to determine whether bacteria, fungi, or archaea are detected in the amniotic fluid of patients who underwent midtrimester amniocentesis for clinical indications. Methods Amniotic fluid samples from 692 pregnancies were tested by using a combination of culture and end-point polymerase chain reaction (PCR) techniques. Intra-amniotic inflammation was defined as an interleukin-6 concentration >2,935 pg/mL. Results Microorganisms were detected in 0.3% (2/692) of cases based on cultivation, 1.73% (12/692) based on broad-range end-point PCR, and 2% (14/692) based on the combination of both methods. However, most (13/14) of these cases did not have evidence of intra-amniotic inflammation and delivered at term. Therefore, a positive culture or end-point PCR in most patients appears to have no apparent clinical significance. Conclusions Amniotic fluid in the midtrimester of pregnancy generally does not contain bacteria, fungi, or archaea. Interpretation of amniotic fluid culture and molecular microbiologic results is aided by the assessment of the inflammatory state of the amniotic cavity. The presence of microorganisms, as determined by culture or a microbial signal in the absence of intra-amniotic inflammation, appears to be a benign condition.

Microbial invasion of the amniotic cavity (MIAC) has been detected in women with preterm labor, preterm prelabor rupture of membranes (PROM), and in patients at term with PROM or in spontaneous labor. Intrauterine infection is recognized as a potential cause of fetal growth restriction; yet, the frequency of MIAC in pregnancies with small-for-gestational-age (SGA) fetuses is unknown. The aim of this study was to determine the frequency, diversity and relative abundance of microbes in amniotic fluid (AF) of women with an SGA neonate using a combination of culture and molecular methods.AF from 52 subjects with an SGA neonate was analyzed with both cultivation and molecular methods in a retrospective cohort study. Broad-range and group-specific PCR assays targeted small subunit rDNA, or other gene sequences, from bacteria, fungi and archaea. Results of microbiologic studies were correlated with indices of the host inflammatory response.1) All AF samples (n=52) were negative for microorganisms based on cultivation techniques, whereas 6% (3/52) were positive based on PCR; and 2) intra-amniotic inflammation was detected in one of the three patients with a positive PCR result, as compared with three patients (6.1%) of the 49 with both a negative culture and a negative PCR (P=0.2).MIAC is detected by PCR in some patients with an SGA fetus who were not in labor at the time of AF collection.