ObjectiveTo assess whether the frequency of adverse neonatal outcome at delivery is related to the level of lactate in amniotic fluid and to the use of oxytocin. DesignProspective observational study. SettingSoder Hospital, Stockholm, Sweden. PopulationSeventy-four women in active labor with a gestational age 36weeks and mixed parity. MethodsLevels of lactate in amniotic fluid were analyzed bedside from an intrauterine catheter every 30min during labor. Deliveries were divided into groups with and without oxytocin. Main outcome measuresThe frequency of adverse neonatal outcome at delivery. ResultOf the deliveries 13.5% (10/74) concluded with an adverse neonatal outcome. The levels of lactate in amniotic fluid increased during labor, more so in deliveries where oxytocin was used. In the group with an adverse neonatal outcome, the level of lactate in amniotic fluid was significantly higher in the final sample before delivery (p=0.04). In 18 deliveries, stimulation with oxytocin was temporarily halted for at least 30min due to overly stimulated labor contractions. A decreasing level of lactate in amniotic fluid was shown within a median 5%/30min. In the group where the administration of oxytocin was halted, there was no adverse neonatal outcome. ConclusionThe frequency of adverse neonatal outcome was associated with the level of lactate in amniotic fluid and with the use of oxytocin. The level of lactate in amniotic fluid may be an additional valuable tool when oxytocin is administered during labor.