Interpretation
Most commonly UA was defined in terms of rate only, as a dichotomous variable and without regard to labour progress. This model is partly based on unavoidable limitations of external tocography but is nonetheless a reductive view of UA which may obscure the effect of increased UA on neonatal outcomes.
The aim of this review was not to assess the impact of UA levels on FHR patterns. However, it is important to consider how interventions for FHR abnormalities might affect the relationship between UA and neonatal outcomes. Three included studies reported increased rates of FHR pattern abnormalities in labours with TS and another (22) reported worsening of FHR traces to be temporally related to TS. In Bofill et al. labours with TS were more likely to result in caesarean delivery for FHR abnormalities. If increased UA leads to fetal distress, interventions for fetal distress such as caesarean delivery might lessen the impact of increased UA and the observed effect on outcome could be weakened. Therefore, differences in the management of TS and/or fetal distress are among the possible explanations for the disparity in reported results. Future studies should report on delivery methods and their indications, as well as any intrauterine resuscitation administered so that these measures can be taken into account.
As an individual marker, it is unlikely that UA can predict the condition of a fetus after delivery. It is possible that increased UA on its own is not typically sufficient to produce significant fetal hypoxia-ischemia, but that in concert with other factors such as placental insufficiency or prolonged labour it may contribute to adverse neonatal outcomes.

Conclusions

Based on current evidence, tachysystole is common and mostly does not result in neonatal complications. There is inconsistent evidence to support the hypothesis that increased UA is associated with neonatal markers of intrapartum hypoxia-ischemia and depressed neurological function in the newborn.