Effect of amniotic fluid bacteria on the course of labor in nulliparous women at term.

Patients with intraamniotic infection have an increased rate of cesarean delivery. To determine whether bacterial colonization of amniotic fluid affects uterine activity or delivery outcome, serial amniotic fluid samples were collected from 41 nulliparous patients in active labor with ruptured membranes for longer than 12 hours. To define positive changes, these samples were divided arbitrarily by colony count change using an increase of less than 10(2) colony-forming units per milliliter; greater than or equal to 10(2) but less than 10(4) colony forming units per milliliter; or greater than or equal to 10(4) colony forming units per milliliter. Nineteen, seven, and 15 sample sets fulfilled these criteria, respectively. Comparing serial samples with these changes in colony count revealed no significant difference in ten labor and delivery variables. Based on virulence of the isolates identified, samples were then divided into high (N = 19) or low (N = 16) virulence in both samples. Compared with sample sets with persistently low-virulence organisms, sample sets with persistently high-virulence isolates had a lower cervical dilatation rate (0.49 +/- 0.39 versus 0.98 +/- 0.58 cm/hour, P = .04), despite an increased maximum oxytocin dose (10.0 +/- 8.0 versus 5.4 +/- 5.2 mU/minute, P = .03). Controlling for birth weight, labor length, and epidural, magnesium sulfate, and oxytocin use, it was found that patients with high-virulence bacteria also had a higher cesarean section rate (57.9 versus 25.0%, P = .05). These results support a causal relationship between high-virulence bacteria in the amniotic fluid and poor cervical dilatation response to oxytocin in patients at risk for the development of intrapartum infection.