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Dr J-C Becher, Department of Neonatology, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Edinburgh EH16 4SA, UK. Email firstname.lastname@example.org
The contribution of intrapartum events to asphyxia-related mortality and morbidity and the degree to which it may be prevented are controversial. We examined trends in asphyxia-related mortality and morbidity in a single large regional perinatal centre. Between 1994 and 2005, the rate of asphyxia fell from 2.86/1000 births in 1994 to 0.91/1000 births in 2005 (P < 0.001). Hypoxic-ischaemic encephalopathy of all grades fell from 2.41 to 0.77/1000 live births (P < 0.001). This substantial and steady fall in the rate of asphyxia-related mortality and morbidity over a 12-year period suggests that a significant proportion of cases of intrapartum asphyxia may be preventable.
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The role of intrapartum events in asphyxia-related mortality and morbidity and the extent to which asphyxia may be preventable are controversial. Nevertheless, the adverse pregnancy outcomes carry substantial personal and economic costs. Obstetric negligence claims account for 50% of all UK medical litigation expenditure and cost the NHS around £200 million a year.1 This has resulted in the quality of intrapartum care receiving scrutiny, particularly by the UK Department of Health, who aimed to reduce obstetric litigation by 25% by 2005.2 Within the UK, research demonstrating a high prevalence of suboptimal intrapartum care among perinatal deaths has prompted a re-examination of delivery room management with the aim of improving pregnancy outcomes.3 However, throughout the world, there is concern that an increase in defensive obstetric practice has resulted in a spiralling of the operative delivery rate.
We aimed to determine whether there has been a change in the prevalence of asphyxia-related mortality and morbidity in our perinatal centre over the past 12 years.
The Simpson Centre for Reproductive Health (previously the Simpson Memorial Maternity Pavilion) in Edinburgh is a large Scottish perinatal centre and delivers nearly 6000 infants per year, accounting for 10% of all Scottish deliveries. From the year 2000, responsibility for the delivery unit moved from a large team of both obstetricians and gynaecologists and became the remit of a small group of specialist high-risk obstetricians. Throughout the 12 years of study, the approach to the resuscitation and management of the asphyxiated newborn remained consistent, and no asphyxiated infant was involved in an interventional study.
Term infants with asphyxia-related mortality and morbidity were defined as those with hypoxic-ischaemic encephalopathy (HIE), or asphyxial delivery room death, or intrapartum stillbirth. Infants who were outborn or who were less than 37 completed weeks of gestation were excluded, as were those with major congenital malformations.
The computerised records of all inborn term (37–43 completed weeks of gestation) admissions to the neonatal unit between January 1994 and December 2005 were searched for codes of ‘hypoxic-ischaemic encephalopathy’, ‘seizures’, ‘fits’, ‘convulsions’ or specific anticonvulsants. Records of all identified cases were retrospectively reviewed to ascertain a diagnosis of HIE, which was defined as an encephalopathy occurring within the first 12 hours of life graded according to Sarnat and Sarnat4 and accompanied by evidence of intrapartum hypoxia-ischaemia (a low cord or initial pH < 7.0 or base deficit ≥ 12 mmol/l, 5 minute Apgar score of ≤5 or evidence of multi-organ involvement). The number of infants with a diagnosis of cerebral infarction or intracerebral haemorrhage was also collected to exclude diagnostic bias during the study period.
The number of term intrapartum stillbirths and the number of term liveborn asphyxiated infants who died in the delivery room following unsuccessful resuscitation were retrieved from hospital statistics and from records reviewed for accuracy of classification. Annual data were collected describing all term hospital deliveries, including maternal age and deprivation score, parity, mode of delivery, infant birthweight, gestation, gender and Apgar scores.
Three-year moving averages were calculated, and trends were analysed with the chi-square test for trend. The t test was used to compare characteristics of the asphyxiated cohort with those of all deliveries. A P value of <0.05 was considered significant. Data were analysed using SPSS for Windows, version 11 (Chicago, IL, USA).
Between 1994 and 2005, there were 63 090 term births. There were 123 cases of asphyxia-related mortality and morbidity, giving an overall rate of 1.95/1000 term births. Figure 1 illustrates the decline in asphyxia-related morbidity and mortality over the study period, from 2.86 to 0.91/1000 term births (P < 0.001). There was a downward trend in all grades of HIE over the study period (grade 1, 1.25–0.3/1000 term births [P < 0.001]; grade 2, 0.88–0.37/1000 term births; grade 3, 0.51–0.18/1000 term births). There was no change in the proportion of term infants with a diagnosis of cerebral infarction or intracerebral haemorrhage.
There were 116 infants with HIE, 5 intrapartum stillbirths and 2 asphyxial delivery room deaths. There were 48 infants with grade 1 HIE, 40 with grade 2 HIE and 28 with grade 3 HIE. Of these 116 infants, 71 (61%) had a low 5-minute Apgar score, 90 (78%) had a low pH and 60 (52%) had evidence of multi-organ failure. Thirty-six infants (31%) had a single feature of intrapartum hypoxic-ischaemia, 40 (34%) had two features and 35 (30%) had 3 features. A further five infants had milder acidosis or depression but with an accompanying sentinel intrapartum event. No infant with asphyxia was born following elective caesarean section.
Infants with asphyxia-related mortality and morbidity were more likely to have a birthweight that was less than the tenth centile compared with all births (30.2 versus 12.3%, P < 0.001). Similar proportions of the asphyxiated cohort and total term population were male (56.5 and 51.2%, respectively) and delivered at or following 41 completed weeks of gestation (29 and 28%, respectively). The proportion of term infants who were of ≥41 completed weeks of gestation increased during the study period from 25.1 to 31.6% (P < 0.001). The annual proportion of male and small-for-gestational-age infants remained constant over time. The percentage of infants with an Apgar score of ≤5 at 1 or 5 minutes remained constant at 4 and 0.4%, respectively.
The percentage of women delivered by instrument or caesarean section increased from 28.1 to 42.7% between 1994 and 2005 (P < 0.001) (Figure 1). Elective caesarean section rose from 4.9 to 9.4% (P < 0.001), emergency caesarean section from 9.6 to 16% (P < 0.001) and instrumental vaginal delivery from 13.6 to 17.3% (P < 0.001). The percentage of women who were aged 35 years or more at delivery increased from 11 to 23% (P < 0.001). The percentage of women in the highest deprivation score category remained constant at 8%, while the percentage of more affluent mothers decreased from 22.2 to 20.8% (P= 0.025). There was no change in the percentage of primigravid women.
These data from a large regional perinatal centre show a marked reduction in asphyxia-related mortality and morbidity over a 12-year period, despite an increasing proportion of older, less affluent mothers and more mature infants. During the same period, there was a marked increase in the operative delivery rate.
A similar reduction in asphyxia in liveborn infants has been reported by others over the past 20 years,5–7 although the contribution of intrapartum stillbirths or delivery room deaths to this rate has not been considered previously. Where many preceding studies have relied on discharge diagnoses for case inclusion, this study involved retrospective review of individual case notes with a variety of related diagnoses to ensure complete and accurate data ascertainment. It is possible that improvements in brain imaging and monitoring in the past 12 years could have resulted in a reduction in the diagnosis of HIE. However, there has not been a concomitant increase in the number of infants diagnosed with other causes of encephalopathy, such as cerebral infarction or intracerebral haemorrhage. This study does not formally investigate the reasons for the decline in asphyxia observed but reports trends in factors known to increase the risk of asphyxia. Although asphyxia is more common in lower socio-economic groups and in older women, these risk factors increased as asphyxia decreased.
A recent study from Bristol showed that training in obstetric emergencies may result in a 50% reduction in low Apgar scores and HIE.8 An audit of strategies employed to minimise obstetric liability within a maternity unit found that the percentage of cases with suboptimal care fell from 74 to 9% during an intervention period.9 Within our centre, developments in clinical practice, such as universal training in cardiotocograph interpretation, a programme of clinical risk management and more specialist consultant input on the delivery suite may have contributed to the trends observed, but the decline in asphyxia-related morbidity and mortality began before these service developments.
Cyr et al.5 reported an inverse relationship between asphyxia and operative deliveries over 20 years ago, but more recent data have shown no reduction in neonatal seizures or perinatal mortality, despite a two-fold increase in the caesarean section rate.10 Others have shown a protective effect of elective caesarean section on neonatal encephalopathy.11,12 Over the period when asphyxia was observed to fall in our study, there was a substantial increase in all modes of operative delivery. However, this observational study cannot determine causation as a trial of different interventions has not been performed, and we have not examined other important aspects of intrapartum management. This would require a study of all deliveries and not just of those associated with cases of asphyxia-related morbidity and mortality.
In conclusion, this study has shown a substantial and steady fall in the rate of asphyxia-related mortality and morbidity over a 12-year period, and this suggests that a significant proportion of cases of intrapartum asphyxia may be preventable.