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.