AMNIOTIC-FLUID COMPLEMENT C3 AS A MARKER OF INTRAAMNIOTIC INFECTION

Objective: To determine the value of amniotic fluid (AF) complement C3 as a marker of intra-amniotic infection and to compare complement C3 with other rapid markers of intra-amniotic infection. Methods: One hun dred four women with singleton gestations, in preterm labor with intac t membranes, at 23-35 weeks' gestation underwent transabdominal amnioc entesis. Amniotic fluid was analyzed for white blood cell (WBC) count, lactate dehydrogenase (LDH), glucose, Gram stain, and complement C3. Cultures for aerobes, anaerobes, and mycoplasma species also were perf ormed. The median values of complement C3, WBC, LDH, and glucose were compared between the culture-positive and -negative groups. Complement W was compared with WBC count LDH, glucose, and Gram stain for sensit ivity, specificity, positive and negative predictive values, and accur acy in the prediction of a positive AF culture. Descriptive statistics , receiver operating characteristic curve, Fisher exact test and Wilco xon rank- sum test were used for analysis. Results: The prevalence of positive cultures was 11.5% (12 of 104). The culture-positive group ha d a significantly higher median C3 (7.0 mg/dL) than the median C3 (3.0 mg/dL)) of the culture-negative group (P <.001). Also, the median val ues of WBC (1120.5 cells/mm(3)) and LDH (2697 UIL) were significantly higher and the median glucose (6.5 mg/dL) was significantly lower amon g women with positive AF cultures than among women with negative AF cu ltures (WBC = 1 cell/mm(3); LDH = 165 U/L; glucose = 45 mg/dL; P < .00 1). Eleven of the 12 culture-positive cases had a C3 of 5 mg/dL or mor e, whereas four of the 92 culture-negative cases had a C3 of 5 mg/dL ( P <.001). Nine of the 12 culture-positive cases but none of the 92 cul ture-negative cases had a C3 of 6 mg/dL or more (P <.001). The relativ e risks of a positive AF culture were 65.27 (95% confidence interval [ CI] 9.08, 469.27) and 31.67 (95% CI 10.40, 96.43) times greater among women with AF complement C3 levels of 5 and 6 mg/dL or more, respectiv ely. Depending on the cutoff point used, complement C3 had similar or higher sensitivity, specificity, positive predictive value, and negati ve predictive value for intra-amniotic infection when compared with WB C count, LDH, glucose and Gram stain Conclusion: Amniotic fluid comple ment C3 has value in the diagnosis of intra-amniotic infection in pret erm labor with intact membranes. Complement C3 is available readily an d compares favorably with other rapid markers of AF infection. This st udy supports the general concept of fetal inflammatory response to mic robial invasion of AF. (C) 1998 by The American College of Obstetricia ns and Gynecologists.