Effect of oxytocin during labor on neonatal acidemia

Objective: To assess the factors affecting neonatal acidemia, including occurrence of tachysystole/hypertonus in fetuses exposed to oxytocin during labour and with continuously-monitored fetal heart rate (FHR) tracings. Methods: Prospective observational study of all women with term pregnancies who received oxytocin for induction/augmentation of labour. FHR tracings were prospectively classified using ACOG classification. Independent predictors of neonatal acidemia were identified using multivariate linear regression with p < 0.05 considered significant. Results: We included 430 women, 236 of whom (54.9%) had spontaneous onset of labour. The duration of active phase of the second stage of labour and the presence of abnormal FHR tracing during labour were significantly associated with UA pH (p < 0.001) and BE (p < 0.001), while maximum dose of oxytocin (p < 0.17; p < 0.7) and tachysystole (p < 0.9; p < 0.8) were not. At logistic regression, the duration of active phase of the second stage of labour was independently predictive of neonatal acidemia (p < 0.009) while abnormal FHR tracing approached significance (p < 0.088). Conclusions: In women receiving oxytocin during labour, the duration of active phase of the second stage of labour correlates with neonatal acidemia, whereas maximum dose of oxytocin, duration of oxytocin administration and occurrence of tachysystole during labour do not.