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.