Intrauterine Pressure Catheter in Labor: Associated Microbiology

Objective: The purpose of this study was to determine if bacterial growth occurred in the amniotic fluid of laboring women. Twenty patients who required an intrauterine pressure catheter (IUPC) during labor were studied. Amniotic fluid samples were aspirated during labor and at the time of delivery. Methods: IUPCs were placed in laboring patients for a variety of reasons. Cervical cultures were taken prior to insertion of an IUPC. After the IUPC was placed, amniotic fluid cultures were taken both at the time of placement and 30 minutes prior to delivery. These cultures were sent for aerobic, anaerobic, Mycoplasma, and Ureaplasma cultures. Results: The increase in bacterial concentration from the initial sample to the final sample was statistically significant (P < 0.01) for both aerobes and anaerobes. Amniotic fluid samples demonstrated a median of 0 bacterial species per patient on initial collection and 2 bacterial species per patient in final collection. The mean count of cfu for erobes in the initial amniotic samples was 3.5 × 104, compared to that of the second samples, which was 1.4 × 105. The mean count of cfu for anaerobes in the initial amniotic fluid samples,.was 4.1 × 102, compared to that of the second samples, which was 8.0 × 103. Only 3 of 20 patients developed chorioamnionitis, with only 1 patient having an increased number ofbacterial species significantly higher than the median. Although 80% of patients had a colony count ≥ 102 cfu/cc, only 19% of this group developed chorioamnionitis. Conclusions: The number of bacterial species and colony counts increased significantly during labor, but this factor alone was not enough to cause chorioamnionitis in a significant number of patients.

3.5 104, compared to that of the second samples, which was 1.4 105. The mean count of cfu for anaerobes in the initial amniotic fluid samples was 4.1 102, compared to that of the second samples, which was 8.0 103. Only 3 of 20 patients developed chorioamnionitis, with only I patient having an increased number of bacterial species significantly higher than the median. Although 80% of patients had a colony count > 102 cfu/cc, only 19% of this group developed chorioamnionitis.
Conclusions: The number of bacterial species and colony counts increased significantly during labor, but this factor alone was not enough to cause chorioamnionitis in a significant number of patients. (C) 1993 Wiley-Liss, Inc. KEY woPs intrauterine pressure catheter, bacterial colonization, amniotic fluid, chorioamnionitis, endomyometritis ntrauterine pressure catheters (IUPCs) are frequently employed to assess labor by monitoring the intensity and frequency of uterine contractions. Recently, the IUPC has been utilized to perform amnioinfusion in situations where the amniotic fluid is significantly decreased to prevent cord compression during uterine contractions. The IUPC may also provide a potential route for endogenous bacteria of the lower genital tract to gain access to the uterine cavity.  The relationship between bacterial colonization of the intrauterine environment and bacterial growth during labor in nulliparous women has been previously described. 5 This study was designed to identify and quantitate the bacterial flora of the intrauterine cavity during labor in patients requiring an IUPC and to examine the effect of time on bacterial colonization.

MATERIALS AND METHODS
This study was conducted on Baylor College of Medicine's Obstetrics Service at Ben Taub General Hospital, a county hospital that serves the indigent and lower socioeconomic population of Harris County, TX. IUPCs were placed in laboring pa-tients for one of the following reasons: dysfunctional labor (50% of patients), trial of labor with history of cesarean section (25%), amnioinfusion on the basis of frequent occurrence of variable decelerations of the fetal heart rate (15%), or the inability to adequately monitor uterine contractions (10%).
Prior to placement of the IUPC, a cervical specimen was collected with a sterile cotton-tipped applicator and placed in anaerobic brain-heart infusion broth transport media. After the IUPC was in place, amniotic fluid was aspirated for the culture of bacteria. The initial 5 cc of amniotic fluid aspirated was discarded. Then, an additional 3 cc was aspirated and placed in anaerobic brain-heart infusion broth transport media. A second specimen was obtained 30 minutes prior to delivery. All specimens were stored at 4C immediately after collection and processed within 24 hours. Remel blood agar, chocolate agar, and McConkey's medium were inoculated for the isolation of aerobic bacteria. The following media were inoculated for the isolation of anaerobic bacteria: CDC blood, KVKDK, and PEACDC agar. A-7 medium was inoculated in an attempt to isolate Mycoplasma and Ureaplasma. Qualitative and quantitative bacteriology were performed on all specimens except Mycoplasma and Ureaplasma as previously described. 6  to compare mean numbers of bacterial isolates and concentrations between the initial and second samples. A two-tailed test was employed with P < 0.05 considered significant. The median numbers of isolates were compared between the initial and second samples using the Wilcoxon rank-sum analysis.

RESULTS
The demographic data of the 20 patients in this study are presented in Table 1. Twelve patients (60%) had a spontaneous vaginal delivery, 4 (20%) had forceps vaginal delivery, and 4 (20%) required cesarean section. Two of the patients who were delivered by cesarean section and one who was delivered by low forceps developed chorioamnionitis (3/20 or 15%). All 3 of these patients had oral body temperatures >38C, elevated WBCs, and uterine fundal tenderness. The WBCs on admission for patient nos. 5, 10, and 14 were 9,200, 11,300, and 9,700, respectively. The WBCs at the time chorioamnionitis was diagnosed were 32,300, 17,300, and 12,000, respectively. No patient developed postpartum endomyometritis.
The spectrum of bacterial species from the cervical cultures at the time of IUPC insertion is shown in Table 2. The bacterial flora of the amniotic fluid collected at the beginning and near the time of delivery are listed in Table 3. Quantitative results from amniotic fluid samples at the two collecting times are summarized in Table 4 (Table  4). The mean number of bacterial species in the initial fluid samples was 0.9 and the median was 0. The mean number of bacterial species in the final fluid samples was 1.8 and the median was 2. The mean count of cfu for aerobes in the initial amniotic fluid samples was 3.5 104, compared to that of the second sample, which was 1.4 l0 s. This increase in bacterial count was statistically significant (P < 0.01). Likewise, the mean count of anaerobic cfu from the first collection was 4.1 102, compared to that of the second sample, which was 8.0 x 103. This increase was also statistically significant (P < 0.01).

DISCUSSION
IUPCs are used in laboring patients for monitoring purposes and for performing amnioinfusions. Because they are placed transvaginally, the possibility exists of introducing vaginal flora into the amniotic cavity. The lower genital tract, especially the vagina, represents a unique microsphere of microbiological life. Surveying the microbiology of the genital tract during labor is important to determine the dynamics of the microbiological ecology of amniotic fluid, e.g., which organisms become dominant and their relationship to the development of chorioamnionitis and endomyometritis. In patients with acute chorioamnionitis, a polymicrobial contamination of the amniotic cavity occurs following rupture of mernbranes and labor. Gilstrap and Cunningham 9 reported a mean per patient of 2.5 microorganisms, 72% of which were gram-positive cocci. In this study, a mean of 0.9 bacterial species was noted, and final samples demonstrated a mean of 1.8 bacterial species per patient. Of the 3 of 20 patients who developed chorioamnionitis in this study, only patient had bacterial species numbers significantly higher than the means noted.
Inoculum size is a significant factor in the development of chorioamnionitis and postpartum endomyometritis. Both Miller et al. 4 and Gibbs et al. 10 demonstrated that intraamniotic infection occurred with greater than 10 2 c(u. While 80% of the patients in our study had colony counts >10 z cfu, only 19% of this group developed chorioamnionitis. Thus, colonization alone appears not to be the only significant factor. According to Larsen et al., 1,12 the amniotic fluid contains an active bacterial inhibitor. It was noted in our study that growth occurred despite this amniotic fluid inhibitor. Although bacterial growth occurs, clinical evidence of an infection does not necessarily ensue. Clinical infection may depend on a number of issues, such as pathogenicity (virulence) and tissue invasion. Concentration may also play a role in this process.
In conclusion, our study demonstrated that both the number of bacterial species and the quantitative cfu increase significantly during labor. This factor alone was not enough to result in chorioamnionitis or postpartum endomyometritis in all patients.