Of the 574 patients studied, a total of 85 patients (14.8%) were found to have infectious morbidity requiring treatment: 67 patients (14.1%) developed endomyometritis; 20 (3.5%) wound infections; nine had documented urinary tract infections; four patients had septic pelvic thrombophlebitis; and two patients developed pneumonia. Some patients developed more than one type of infection. Most cases of infectious morbidity were in the nonelective cesarean group (n = 66 nonelective, n = 19 for elective group) (18.3% versus 8.9%, P < .001; relative risk [RR] = 0.4 [95% confidence interval (CI) 0.3, 0.7]). Twelve cases of endomyometritis occurred in the elective group, whereas 55 were in the nonelective group (P < .001; RR = 0.3 [95% CI 0.2, 0.6]). Two wound infections, one urinary tract infection, and one case of septic pelvic thrombophlebitis occurred in the elective cesarean group. One case of pneumonia occurred in each group. No significant differences were seen between cesarean groups with respect to these subgroups of infection.
Table 3 shows the risk factors that showed significant differences in patients having a nonelective cesarean depending on the development or not of an infection. Variables tested but not found to have any significant differences include length of membrane rupture, type of anesthesia, length of bladder catheterization, presence of meconium-stained amniotic fluid, use of prophylactic antibiotics, type of skin incision, type of uterine incision, estimated blood loss, postpartum hemorrhage, Apgar scores, birth weight, umbilical artery cord pH, NICU admission, maternal smoking, drug abuse, insurance type, presence of maternal diabetes, maternal age, and gestational age at delivery. Nonwhite ethnicity, obesity, greater BMI, longer time in labor, greater number of digital examinations, professional level of the operator, and primary cesarean were all more frequently present in those developing infection. The RR for an obese patient to develop an infection postcesarean was 3.0 (95% CI 1.6, 5.8). Obese patients were more likely to develop endomyometritis (15.9% versus 5.0%, P < .001; RR = 3.3 [95% CI 1.6, 6.9]). Though not significant, 75% of the wound infections also occurred in the obese patient group. In addition, when evaluating only patients who received prophylactic antibiotics (n = 265), obese patients still had the greater risk of developing endomyometritis (14.5% versus 4.4%, P < .001; RR = 3.9 [95% CI 1.7, 9.0]). The risk for developing any infection also remained higher even when antibiotic prophylaxis was provided for the obese patient (23.4% versus 8.5%, P < .001; RR = 3.3 [95% CI 1.6, 6.8]). No differences were seen in infection rates between obese and nonobese patients who were not given antibiotic prophylaxis (n = 47) (23.1% versus 14.2%, RR = 1.8 [95% CI 0.4, 8.3]).
Patients undergoing a cesarean for cephalopelvic disproportion or failure to dilate (n = 134) (as opposed to all other indications) had a higher incidence of infectious morbidity (27.1% versus 11.9%, P < .001; RR = 2.7 [95% CI 1.5, 4.9]). The incidence of infection in patients undergoing cesarean for cephalopelvic disproportion (n = 90) was even higher than in those who had other cesarean indications (34.4% versus 10.8%, P < .001; RR = 4.3 [95% CI 1.4, 13.6]).
Only BMI, maternal obesity, length of labor, and the mean number of digital cervical examinations remained significant as potential risk factors of postcesarean infectious morbidity after multivariate analysis. Receiver operating characteristic (ROC) curves were determined for BMI, length of labor, and the number of digital examinations. For BMI, the area under the curve was 0.678 (0.602–0.753, P < .001). For a BMI greater than 30, the sensitivity was 85.1%, and the specificity was 55.8%. With respect to prediction of infectious morbidity, the ROC curve for labor length suggested a cut point of 10 hours for increased risk for infectious morbidity (sensitivity 67.3%, specificity 50.0%). The area under the curve was 0.663 (0.579–0.747, P < .001). A cut point of four or more examinations was associated with an increased risk for infection (sensitivity 72.7%, specificity 55.4%). The area under the curve for digital examination and the occurrence of infectious morbidity was 0.614 (0.529–0.699, P < .001).
Table 4 contains the significant risk factors for infectious morbidity for those patients having an elective cesarean. Other variables tested but not showing significant difference included number of digital examinations, gestational age at delivery, type of skin incision, maternal tobacco usage, maternal insurance type, maternal drug abuse, maternal diabetes, type of anesthesia, total operative time, length of bladder catheterization, presence of meconium-stained amniotic fluid, estimated blood loss, incidence of postpartum hemorrhage, birth weight, Apgar scores, umbilical artery cord pH, and NICU admission. The increased risks for infectious morbidity associated with maternal race (black) and BMI remained after multivariate analysis. No risk was seen with respect to professional level of the primary surgeon when one controls for the use of antibiotic prophylaxis. The use of prophylactic antibiotics reduced the risk for postoperative infection in the residents' cases. If one controls only for obesity, more postcesarean infections were seen with the residents' patients. This risk could be race-related, as black patients had higher rates of infection. The relative risk for postoperative morbidity in an obese patient having an elective cesarean is 1.6 (95% CI 1.2, 2.0). For the obese patient not given prophylactic antibiotics, the risk is increased significantly to 2.5 (95% CI 1.3, 4.9). The ROC curve for BMI and the occurrence of some type of infectious morbidity was determined. For a BMI greater than 30.0, the sensitivity was 90.0%, and the specificity was 58.0%. The area under the curve was 0.737 (0.613–8.60, P < .001).
Based on our MEDLINE search of literature from 1966 to April 2002, our finding of an increased risk for infectious morbidity in obese patient regardless of elective or nonelective nature of cesarean had not been previously reported. Knowledge that the risk of infectious morbidity is increased 2–3 times in obese patients undergoing cesarean is important. Our study has confirmed the reports of both Tran and colleagues14 and Perlow and Morgan,15 who each noted an increased incidence of postcesarean infectious morbidity in the nonelective delivered obese patient. Chauhan et al17 noted more infectious morbidity in patients of 300 or more pounds who had a failed vaginal birth after cesarean delivery attempt when compared with a similar group having an elective repeat cesarean delivery. Their numbers were limited, and no control group was described. Our postcesarean infectious morbidity rate of 14.8% in obese patients is within the 12.4%–23.3% range previously reported.14 Our study also confirms that, in spite of the use of prophylactic antibiotics, obese patients have higher rates of infectious morbidity. This raises clinical questions related to current prophylactic doses, the time of administration, and perhaps the need for a more prolonged administration of antibiotics. Because obesity was the most important risk factor for postoperative infection identified in this study, and because it is one of the few risk factors that cannot be avoided when a patient presents in labor, education to minimize excessive prenatal weight gain, recommendations for preconceptual weight loss, and studies investigating alternative prophylactic treatments are needed. The ROC curves generated in this study would seem to suggest using a BMI cut point of 30.0 to design these studies.
Knowledge of who is at increased risk for infectious morbidity should impact labor management. Early intervention with oxytocin has been shown to reduce infectious morbidity.18,19 The risk for increased intrauterine infections associated with more frequent digital examinations of the cervix has also been described.20,21 Steps to reduce the frequency of digital examinations of the cervix would also seem warranted, particularly in light of the work of Imseis and coworkers.22 They found that a single digital examination nearly doubled the number of different types of organisms cultured from the cervix. Our data suggest that attempts to both shorten the length of labor to less than 10 hours by administration of oxytocin and performing less than four digital examinations could decrease the risk of infection if the patient requires a cesarean.
We also noted an increased risk of infection in black women undergoing elective cesarean. Corrections for obesity and antibiotic usage did not eliminate this risk. This would seem to be consistent with a review of the literature by Fiscella23; however, the increased risk for infectious morbidity for blacks was lost after multivariate analysis in the nonelective cesarean group. A possible explanation for the higher infection rates seen in patients of this ethnicity may have to do with higher colonization rates for group B streptococci.24,25 Because less than 50% of our patients had group B streptococci screening performed, adequate comparisons could not be made for this factor; however, all patients were treated preoperatively if either a positive culture result or presence of group B streptococci risk factors were found in accordance with the recommendations of the American College of Obstetricians and Gynecologists.26 We did not make comparisons between groups for chlamydia, gonorrhea, or bacterial vaginosis. Patients found to have chlamydia or gonorrhea prenatally were treated at diagnosis. Test of cures were done after treatment. We were not able to locate any studies suggesting a different frequency of these infections in the obese patient; however, the higher postoperative infection rates seen in this study for the obese population would also suggest further evaluations for these pathogens.
We did not evaluate the method of placental delivery, owing to poor documentation. The same holds true for the management of the visceral peritoneum and timing of antibiotic administration. Very few subcutaneous drains were documented in the hospital records, so no analysis could be done for this variable. The importance of each of these infection-preventing techniques necessitates further evaluation in the obese patient. Until such studies are made, one could consider making use of each of these techniques in order to further minimize the risk of postoperative infection in the obese patient.
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© 2002 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
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