Uterine contraction frequency during treatment of pyelonephritis in pregnancy and subsequent risk of preterm birth

To assess ceftriaxones effect on uterine contraction frequency and determine risk factors for subsequent preterm birth in women with pyelonephritis. Seventy-one women with pyelonephritis at greater than 24 weeks' gestation with continuous external tocodynamometry after antibiotic administration were studied. Patients received 2 doses of ceftriaxone 1 gram intramuscularly at 24-hour intervals. Temperatures, timing of antibiotic administration, and gestational age at delivery were recorded. Uterine contraction frequency was measured for the hour prior to antibiotic administration, as well as the six hours after. Uterine activity steadily and significantly decreased from a mean of 5.1 +/- 7.3 at presentation to 2.0 +/- 2.9 uterine contractions per hour (P = .04, student t-test) six hours after ceftriaxone administration. The maximal number of contractions per hour each woman experienced did not correlate with temperature (r = .02, linear regression analysis). Uterine contractility and recurrent urinary tract infection were both associated with subsequent preterm birth (P = .004 and .016 respectively using nominal logistic regression analysis). (1) A significant decrease in uterine activity from baseline occurs after ceftriaxone administration for acute pyelonephritis in pregnancy. (2) Temperature elevations are not associated with increased uterine activity. (3) Patients with significant uterine activity or recurrent urinary tract infection are at risk for preterm birth.