Objective. Chorioamnionitis complicates 1% to 10% of pregnancies and increases the risk of neonatal infection. Women with chorioamnionitis receive intrapartum antibiotics, often resulting in inconclusive neonatal blood cultures. Peripheral neutrophil values are used frequently to assist in the diagnosis of neonatal infection and to determine duration of antibiotics; we sought to determine the utility of this approach.

Methods. A prospective observational study was performed in 856 near-term/term neonates who were exposed to suspected chorioamnionitis. Each received antibiotics for 48 hours unless clinical infection or positive blood cultures occurred. Peripheral neutrophils were measured serially and analyzed using the reference ranges of Manroe et al; an additional analysis of only the initial neutrophil values used the normal ranges of Schelonka et al. Results of neutrophil analyses were not used to determine duration of therapy. Fifty percent of asymptomatic neonates were seen postdischarge to ascertain recurrent infection. Local patient charges were examined.

Results. Ninety-six percent of neonates were asymptomatic and had negative cultures, and antibiotics were discontinued at 48 hours. A total of 2427 neutrophil counts were analyzed. Although abnormal neutrophil values were more frequent in infected or symptomatic neonates, 99% of asymptomatic neonates had ≥1 abnormal value. The specificity and negative predictive values for abnormal neutrophil values ranged between 0.12 and 0.95 and 0.91 and 0.97, respectively; sensitivity was 0.27 to 0.76. Significant differences in interpretation of the initial neutrophil values were noted, depending on the normal values used. Follow-up was performed for 373 asymptomatic neonates until 3 weeks’ postnatal age. Eight required rehospitalization; none had evidence of bacterial infection. If neutrophil values had been used to determine duration of antibiotics, then local costs would have increased by $76 000 to$425 000 per year.

Conclusions. Single or serial neutrophil values do not assist in the diagnosis of early-onset infection or determination of duration of antibiotic therapy in asymptomatic, culture-negative neonates who are ≥35 weeks’ gestation and are delivered of women with suspected chorioamnionitis.