Strengths and Limitations
The National Birth Registry of Austria is maintained by obstetric
departments, therefore collected information mainly focuses on obstetric
and gynaecologic rather than on anaesthesiologic aspects. No information
on cervical dilatation or timepoint of the application of EA, as well as
a differentiation of duration of birth between first and second stage of
labour, is recorded. Further, type of local anaesthetic, dosage and
application modality (bolus, patient-controlled EA, programmed
intermittent epidural bolus, dural puncture epidural) for EA is not
documented, making it difficult to draft assumptions about the impact of
EA technique on the altered outcome variables. It is described that
epidural related maternal fever occurs frequently and was shown to be
associated with worse neonatal outcome. Maternal body temperature is
unfortunately not incorporated in the registry, so an association of EA
and maternal fever could not be investigated in this analysis. The use
of oxytocin for labour augmentation is also not available. Obstetricians
may adapt their procedural decision on the presence of adequate pain
relief, which could lead to higher rates of instrumental vaginal
deliveries and episiotomies. This bias could not be considered in the
statistical models. Outcome variables were sufficiently reported, except
for BE, which was missing in 23.5%, although, missing data were equally
distributed between EA (22.4%) and noEA (23.8%). All hospitals
registered for obstetric services in Austria provide data to the
National Birth Registry, representing 98% of annual births. The
analysed data is therefore close to the basic population of primiparous
women with spontaneous vaginal delivery at term, thereby avoiding a
meaningful selection bias.