Discussion
This study from three referral hospitals found that the majority of HIE
cases over a 10-year period were delivered >120 minutes
after presentation and did not result from sentinel events. Most cases
had moderate variability, accelerations, or both on presentation, and of
the cases with these FHR characteristics on presentation not delivered
within 120 minutes or for a sentinel event, 40% also had moderate
variability and/or accelerations, prior to delivery. Among the group of
women with moderate variability, accelerations, or both prior to
delivery 30% had a prolonged second stage, and significant proportions
delivered either via pre-labor cesarean (26%) or vaginally with a
second stage <1 hour (22%). Paradoxically, women who
delivered >120 minutes after presentation with moderate
variability and/or accelerations, on presentation were more likely to
deliver by cesarean with moderate variability and/or accelerations,
prior to delivery, although this difference was not statistically
significant.
The findings from this study support the diverse clinical scenarios and
labor characteristics associated with HIE and there was no common theme
identified that could predict any significant proportion of HIE cases.
Studies from the UK13, South
Africa14 and New Zealand15 have
estimated the degree to which intrapartum asphyxia was associated with
human factors and found preventability in 64%, 63% and 55% of cases
respectively. In 38% of the cases in this study, delivery occurred in
the absence of moderate variability or accelerations after these
features were noted on presentation supporting the possibility of acute
events occurring during labor. Of the 26% of cases that occurred with
moderate variability and/or accelerations, proximal to delivery more
than a quarter had a labor duration of ≥18 hours supporting the
possibility that other approaches, such as the use of category II
algorithms, may be required to ascertain risk beyond the presence or
absence of variability or accelerations alone.5Overall these findings support the notion that risk reduction for HIE
will likely require care improvement and management across a range of
clinical scenarios, and that some outcomes may be unpreventable.
Clinical chorioamnionitis and fetal growth restriction diagnoses were
not particularly common among pregnancies resulting in HIE in the
setting of FHR findings demonstrating moderate variability,
accelerations, or both, and thus were unlikely to be important
explanatory risk factors in this case series.
This study evaluated a large number of cases of HIE in three different
academic medical centers. Factors leading to HIE may be challenging to
study due to its infrequent clinical occurrence. The relatively large
number of cases evaluated in this study allowed us to create reasonably
sized groups describing labor and delivery management and risk factors,
as well as fetal heart tracing characteristics that allow meaningful
clinical interpretations. That we were able to include detailed data on
each case facilitated comparisons across a number of clinical management
parameters.
Limitations include that while the review of each case of HIE involved
the thorough examination of the healthcare record by an individual
researcher it is certainly possible that due to the retrospective nature
of data collection some relevant material may have been omitted or
inaccurately recorded. A prospective design with contemporaneous
recording and a validated data collection tool may have improved the
accuracy of the reported data.