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Background Progress in reducing late fetal deaths has slowed in recent years, despite changes in intrapartum and antepartum care.
Objectives To describe recent trends in cause-specific fetal death rates.
Design Retrospective cohort study.
Setting North of England.
Population/Sample 3,386 late fetal deaths (≥28 weeks of gestation and at least 500 g), occuring between 1982 and 2000.
Methods Data on deaths were obtained from the Northern Perinatal Mortality Survey. Data on live births were obtained from national birth registration statistics. Rate ratios (RR) and 95% confidence intervals (CI) for fetal deaths in 1991–2000 compared with 1982–1990 were calculated.
Main outcome measures Cause-specific late fetal death rates per 10,000 total births.
Results Mortality in singletons declined from 51.5 per 10,000 births in 1982–1990 to 42.0 in 1991–2000 (RR 0.82, 95% CI 0.76–0.87). There was a greater decline in multiples, from 197.9 to 128.0 per 10,000 (RR 0.65, 95% CI 0.51–0.83). In singletons, the largest reductions occurred in intrapartum-related deaths, and deaths due to congenital anomalies, antepartum haemorrhage and pre-eclampsia. There was little change in the rate of unexplained antepartum death occurring at term (RR 0.97, 95% CI 0.84–1.11) or preterm (RR 0.94, 95% CI 0.82–1.07), these accounting for about half of all late fetal deaths. Unexplained antepartum deaths declined in multiple births and in singletons of birthweight <1500 g.
Conclusions While late fetal mortality due to many specific causes has declined, unexplained antepartum death rates have remained largely unchanged. Improved identification of deaths due to growth restriction and infection, which may otherwise be classified as unexplained, is important. Further investigation of the underlying aetiologies of genuinely unexplained deaths is needed.
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Late fetal deaths, occurring after 28 weeks of gestation, remain a persistent and challenging problem. Progress in reducing these deaths has slowed in recent years.1,2 Over the past two decades, many changes have taken place to both intrapartum and antenatal care within the UK. Rates of operative and other interventions in labour and delivery have risen substantially, and the proportion of vaginal deliveries is reducing.3 Antenatal care, in contrast, has been increasingly devolved to community-based health professionals.4
Examination of recent trends in antepartum and intrapartum fetal deaths, and of the underlying causes of these deaths, is necessary, to direct future preventive and research effort. Many late fetal deaths remain unexplained, however,1,5 and this makes the identification of specific preventive strategies difficult.
The Northern Perinatal Mortality Survey provides a large, well-validated database of fetal deaths within a geographically defined population, with consistent cause of death classification and a relatively high autopsy rate. The aim of this study was to describe the underlying causes of late fetal deaths, and to investigate changes in cause specific fetal death rates over the past two decades.
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Late fetal deaths were defined as stillbirths occurring after 28 completed weeks of gestation and weighing at least 500 g. Twenty-eight weeks was used in the case definition, rather than 24 weeks, which has defined a legally registrable stillbirth in England and Wales since 1992, to promote consistency over the study period. Births weighing less than 500 g were excluded in line with WHO recommendation.
All such deaths occuring between 1982 and 1990 were identified from the Northern Region Perinatal Mortality Survey, and data relating to the timing and cause of death, birthweight, number of fetuses in the pregnancy, and whether autopsy was undertaken were obtained. The Perinatal Mortality Survey is a population-based survey of fetal deaths (20 weeks onwards) and deaths in infancy to mothers resident in the former Northern region of England—a population of 3.1 million with an average 36,000 births per year during the study period. There are 19 maternity units within the region, ranging from small midwife-led units to large tertiary centres, but the majority of births during the study period occurred in district consultant-led maternity units delivering between 1000 and 3000 babies per year.6 Notification of cases to the Perinatal Mortality Survey is from multiple sources, ensuring high case ascertainment; data collection and validation methods have been described previously.7
Data on all registered live births occurring between 1982 and 2000, and weighing at least 500 g, were obtained from the Office for National Statistics. These were merged with Perinatal Mortality Survey fetal deaths data to form a single data set. Office for National Statistics data on registered stillbirths were not used, because annual cross-validation checks show that Perinatal Mortality Survey identification of stillbirths is more complete than national registration data.6
Cause of death is assigned by a multidisciplinary review team within each maternity unit, and reviewed by the Perinatal Mortality Survey clinical director to ensure consistency of coding. Causes of death are coded in the Perinatal Mortality Survey database using both the Aberdeen classification of obstetric causes8 and the extended Wigglesworth clinico-pathological classification of fetal and neonatal factors,9 providing details of both maternal and fetal factors contributing to death.
For this study, cause of death according to the Aberdeen classification was combined with information about the timing of death (whether before or during labour) to create cause of death categories (Table 1). This enabled the separate identification of important obstetric antecedents of fetal death such as antepartum haemorrhage, pre-eclampsia and pre-existing maternal conditions. Detailed diagnoses for deaths due to infection, maternal conditions and other specific conditions were obtained from autopsy and other paper records held by the Perinatal Mortality Survey.
Table 1. Cause of late fetal deaths in singleton and multiple pregnancies, and autopsy rates. Values are presented as n (%).
|Cause of death category||Late fetal deaths by cause||Fetal deaths with autopsy|
|Congenital anomaly (any genetic or structural defect causing death)||240 (7.7)||30 (12.0)||195 (72.2)|
|Antepartum haemorrhage (abruption and placenta praevia)||574 (18.3)||10 (4.0)||318 (54.5)|
|Pre-eclampsia (with proteinuria and no pre-existing hypertensive disease)||185 (5.9)||12 (4.8)||140 (71.1)|
|Intrapartum-related deaths (includes birth trauma)|
|Malpresentation or disproportion||32 (1.0)||7 (2.8)||22 (56.4)|
|Cord prolapse or compression||29 (0.9)||0||12 (41.4)|
|Uterine rupture||8 (0.3)||0||1 (12.5)|
|Unexplained intrapartum death (includes deaths during preterm labour)||163 (5.2)||12 (4.8)||126 (76.0)|
|Unexplained antepartum death|
|Unexplained preterm (<37 weeks)||829 (26.4)||84 (33.5)||738 (80.8)|
|Unexplained term (≥37 weeks)||784 (25.0)||46 (18.3)||666 (80.2)|
|Hypertension (pre-existing)||35 (1.1)||1 (0.4)||27 (75.0)|
|Diabetes||54 (1.7)||3 (1.2)||48 (84.2)|
|Other (includes renal disease, liver disease and trauma)||25 (0.8)||0||17 (68.0)|
|Other specific conditions|
|Infection||44 (1.4)||2 (0.8)||34 (73.9)|
|Isoimmunisation||24 (0.8)||0||23 (95.8)|
|Twin-to-twin transfusion syndrome||0||41 (16.3)||33 (80.5)|
|Fetal hydrops (unknown cause)||24 (0.8)||0||22 (91.7)|
|Fetal blood loss (includes vasa praevia and feto-maternal transfusion)||18 (0.6)||0||14 (77.8)|
|Fetal tumour||6 (0.2)||1 (0.4)||7 (100.0)|
|Antepartum death with cord compression||43 (1.4)||2 (0.8)||28 (62.2)|
|Other||10 (0.3)||0||9 (90.0)|
|Unclassifiable||8 (0.3)||0||8 (100.0)|
|All causes||3135 (100.0)||251 (100.0)||2488 (73.5)|
Cause-specific late fetal death rates were calculated per 10,000 total births. Analysis of time trends was undertaken by comparing rates in 1991–2000 with 1982–1990, dividing the study period into time periods with similar numbers of births. Rate ratios (RR) and 95% confidence intervals (CI) were calculated, and statistical significance was accepted at the 5% level. Analysis was carried out using STATA 8.0.
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Between 1982 and 2000, a total of 3386 fetal deaths delivered at 28 weeks of gestation or greater and weighing at least 500 g were reported to the Perinatal Mortality Survey. Of these, 2881 (85%) occurred before the onset of labour.Figure 1 shows trends in antepartum and intrapartum deaths over the study period. The intrapartum death rate halved between 1982–1990 and 1991–2000, from 9.7 to 5.0 per 10,000 births (RR 0.52, 95% CI 0.43–0.63). In contrast, the antepartum death rate declined by only 13%, from 44.8 to 39.1 per 10,000 births (RR 0.87, 95% CI 0.81–0.94).
The overall autopsy rate was 74%(Table 1). Autopsy rates were particularly high for unexplained antepartum deaths (80%). The lowest rates were for deaths following antepartum haemorrhage (55%) and for explained intrapartum-related deaths (13–56%). The autopsy rate declined over time, from 79% for deaths occurring between 1982 and 1990 to 67% for those occurring in 1991–2000 (difference in proportions 12%; 95% CI 9–15%). Between 1982 and 1990, the autopsy rate was maintained at a high level, but since 1991 there has been a steady and continuing decline (data not shown).
The cause of death remained unclassifiable in eight cases, all of which underwent autopsy. Seven of these were unattended deliveries (no paper record could be located for the remaining case), all but one of which came to light when the baby's abandoned body was found.
In singleton pregnancies, the overall late fetal death rate was 46.8 per 10,000 births. Fifty-one percent of deaths in singletons were unexplained antepartum deaths, of which about half occurred at term (Table 1). Of the 505 deaths occurring during labour, 251 (50%) were classified as intrapartum-related, with the remainder due to conditions where the timing of death was not relevant to the assignment of cause of death, such as congenital anomalies.
Multiple births accounted for 2.3% of births and 7% of late fetal deaths (Table 1). The overall late fetal death rate was 159.4 per 10,000 births (RR compared with singletons 3.41; 95% CI 3.00–3.87). The distribution of causes of death differed compared with singletons (Table 1). There was a similar proportion of unexplained antepartum deaths (52%), but nearly two-thirds of these occurred preterm. Sixteen percent of deaths in multiple births were attributed to twin-to-twin transfusion syndrome.
Forty-six deaths were due to infection. The most frequent organism identified was group B streptococcus (15 cases; 33%). In a further eight cases, the cause of death was reported as ‘chorioamnionitis’, with no organism identified. A wide range of infections was recorded for the remaining deaths, including cytomegalovirus (five cases), Listeria monocytogenes (four cases), Escherichia coli and staphylococcus (two cases each).
Of the 25 deaths attributed to maternal conditions other than diabetes or hypertension, eight were due to maternal liver disease, six to trauma or accidents and five to renal disease.
In singletons, the all cause late fetal death rate declined from 51.5 per 10,000 births in 1982–1990 to 42.0 in 1991–2000 (RR 0.82, 95% CI 0.76–0.87). The rate of decline varied by cause of death (Table 2). There was a substantial reduction in intrapartum-related deaths, particularly for deaths due to malpresentation and cord prolapse. Deaths due to congenital anomalies declined by nearly half (RR 0.54, 95% CI 0.42–0.71), while deaths due to antepartum haemorrhage and pre-eclampsia showed smaller but highly significant reductions. In contrast, the rate of unexplained antepartum death remained largely unchanged between the two time periods.
Table 2. Cause-specific death rates* and rate ratios§ for late fetal deaths in 1991–2000 compared with 1982–1990. Values are presented as rate (no. of deaths) and rate ratio (95% CI).
| ||Singleton births||Multiple births|
|1982–1990 (n= 334,728)||1991–2000 (n= 334,381)||Rate ratio (95% CI)||1982–1990 (n= 7074)||1991–2000 (n= 8674)||Rate ratio (95% CI)|
|Congenital anomaly||4.6 (156)||2.5 (84)||0.54 (0.42–0.71)||19.8 (14)||18.4 (16)||0.93 (0.46–1.91)|
|Antepartum haemorrhage||10.2 (342)||6.9 (232)||0.68 (0.58–0.81)||5.7 (4)||6.9 (6)||–|
|Pre-eclampsia||3.5 (116)||2.1 (69)||0.60 (0.44–0.81)||15.6 (11)||1.2 (1)||–|
|Malpresentation or disproportion||0.7 (25)||0.2 (7)||0.28 (0.12–0.65)||8.5 (6)||1.2 (1)||–|
|Cord prolapse or compression||0.6 (21)||0.2 (8)||0.38 (0.17–0.86)||0||0||–|
|Uterine rupture||0.1 (4)||0.1 (4)||–||0||0||–|
|Unexplained intrapartum death||3.1 (105)||1.7 (58)||0.56 (0.40–0.77)||11.3 (8)||4.6 (4)||–|
|Unexplained antepartum death|
|Unexplained preterm||12.8 (429)||12.0 (400)||0.94 (0.82–1.07)||59.4 (42)||48.4 (42)||0.82 (0.53–1.25)|
|Unexplained term||11.9 (400)||11.5 (384)||0.97 (0.84–1.11)||39.6 (28)||20.8 (18)||0.52 (0.29–0.95)|
|Hypertension||0.7 (22)||0.4 (13)||0.59 (0.30–1.18)||1.4 (1)||0||–|
|Diabetes||1.0 (32)||0.7 (22)||0.69 (0.40–1.19)||2.8 (2)||1.2 (1)||–|
|Other||0.4 (12)||0.4 (13)||1.09 (0.50–2.39)||0||0||–|
|Other specific conditions|
|Infection||0.4 (13)||0.9 (31)||2.40 (1.25–4.58)||2.8 (2)||0||–|
|Isoimmunisation||0.4 (15)||0.3 (9)||0.60 (0.26–1.38)||0||0||–|
|Twin-to-twin transfusion||–||–||–||31.1 (22)||21.9 (19)||0.70 (0.38–1.30)|
|Fetal hydrops||0.3 (10)||0.4 (14)||1.41 (0.63–3.17)||0||0||–|
|Fetal blood loss||0.1 (5)||0.4 (13)||–||0||0||–|
|Fetal tumour||0.1 (4)||0.06 (2)||–||0||1.2 (1)||–|
|Antepartum death with cord compression||0.4 (15)||0.8 (28)||1.88 (1.00–3.51)||0||2.3 (2)||–|
|Other||0.1 (5)||0.2 (5)||–||0||0||–|
|All causes (including unclassified)||51.5 (1731)||42.0 (1404)||0.82 (0.76–0.87)||197.9 (140)||128.0 (111)||0.65 (0.51–0.83)|
Deaths attributed to infection, although accounting for a very small proportion of late fetal deaths in singletons (2.2%), showed a significant twofold increase (RR 2.40, 95% CI 1.25–4.58). Antepartum deaths attributed to cord compression also increased between the two time periods, although this was of borderline significance, probably due to the small number of deaths (RR 1.88, 95% CI 1.00–3.51).
In multiple births, the overall late fetal death rate declined by about a third between 1982–1990 and 1991–2000, from 197.9 per 10,000 to 128.0 (RR 0.65, 95% CI 0.51–0.83). In contrast to singletons, there was a significant reduction in the unexplained antepartum death rate at term, but not before term (Table 2). The death rate due to congenital anomalies showed no significant change, unlike that for singletons.
Table 3 shows trends in cause-specific fetal death rates by birthweight category, for singletons. The decline in overall mortality was confined to low birthweight babies (birthweight categories 500–1499 and 1500–2499 g). Among normal birthweight babies (≥2500 g), only deaths due to congenital anomalies and intrapartum-related deaths showed significant reductions over time. Unexplained antepartum deaths accounted for similar proportions of late fetal deaths in all birthweight categories (52% at birthweights 500–1499 g, 49% at 1500–2499 g and 53% at ≥2500 g). There was a significant reduction in these deaths in the lowest birthweight category only, the rates remaining largely unchanged over time within heavier birthweight categories (RR 0.94, 95% CI 0.79–1.12 for birthweights 1500–2499 g; RR 1.02, 95% CI 0.88–1.19 for birthweights ≥2500 g).
Table 3. Cause-specific death rates* and rate ratios§ for late fetal deaths in 1991–2000 compared with 1982–1990, by birthweight category, singletons only. Values are presented as rate (no. of deaths) and rate ratio (95% CI).
|Cause of death||1982–1990||1991–2000||Rate ratio (95% CI)|
|Birthweight 500–1499 g||n= 2776||n= 3097|| |
|Congenital anomaly||212.5 (59)||90.4 (28)||0.42 (0.27–0.67)|
|Antepartum haemorrhage||295.4 (82)||180.8 (56)||0.61 (0.44–0.86)|
|Pre-eclampsia||223.3 (62)||100.0 (31)||0.45 (0.29–0.69)|
|Intrapartum-related deaths||28.8 (8)||35.5 (11)||–|
|Unexplained antepartum deaths||842.9 (234)||639.3 (198)||0.76 (0.63–0.91)|
|Maternal conditions||79.3 (22)||38.7 (12)||0.49 (0.24–0.99)|
|Other specific conditions||32.4 (9)||48.43 (15)||1.49 (0.65–3.41)|
|All causes||1714.7 (476)||1136.6 (352)||0.66 (0.58–0.75)|
|Birthweight 1500–2499 g||n= 17,374||n= 17,449|| |
|Congenital anomaly||28.2 (49)||17.8 (31)||0.63 (0.40–0.99)|
|Antepartum haemorrhage||90.9 (158)||49.3 (86)||0.54 (0.42–0.70)|
|Pre-eclampsia||22.4 (39)||14.3 (25)||0.64 (0.39–1.05)|
|Intrapartum-related deaths||17.8 (31)||4.6 (8)||0.26 (0.12–0.56)|
|Unexplained antepartum deaths||145.0 (252)||135.8 (237)||0.94 (0.79–1.12)|
|Maternal conditions||10.4 (18)||8.6 (15)||0.83 (0.42–1.65)|
|Other specific conditions||12.7 (22)||18.3 (32)||1.45 (0.84–2.49)|
|All causes||326.9 (568)||248.7 (434)||0.76 (0.67–0.86)|
|Birthweight ≥ 2500 g||n= 314,464||n= 312,112|| |
|Congenital anomaly||1.5 (48)||0.8 (25)||0.52 (0.32–0.85)|
|Antepartum haemorrhage||3.2 (102)||2.9 (90)||0.89 (0.67–1.18)|
|Pre-eclampsia||0.5 (15)||0.4 (13)||0.87 (0.42–1.94)|
|Intrapartum-related deaths||3.7 (116)||1.9 (58)||0.50 (0.37–0.69)|
|Unexplained antepartum deaths||10.9 (343)||11.1 (349)||1.02 (0.88–1.19)|
|Maternal conditions||0.8 (26)||0.7 (21)||0.81 (0.46–1.45)|
|Other specific conditions||1.2 (37)||1.8 (55)||1.50 (0.99–2.27)|
|All causes||21.8 (687)||19.8 (618)||0.91 (0.81–1.01)|
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In our population, there has been a modest but significant decline in the late fetal death rate over the past two decades. There were marked differences in the rate of decline for different cause categories, however, and for some subgroups of births.
The overall autopsy rate of 74% compares favourably to other UK regions,1,10,11 and is close to the nationally recommended rate of 75%.12 In recent years, in common with other areas of the UK, the rate has declined, and there has been concern over the quality of some autopsies, particularly in earlier years.13 Some caution must be exercised when interpreting trends in cause-specific fetal death rates in the presence of a falling autopsy rate, because autopsy can change the recorded cause of death.11,14 It is reassuring that in our study, unexplained deaths had particularly high rates of autopsy. The continuing decline in autopsy rates, however, is of wider concern, as failure to investigate the underlying causes of fetal deaths will hamper efforts to understand and prevent future mortality.
The Perinatal Mortality Survey consistently identifies a small number of additional fetal deaths compared with those reported by the Office for National Statistics. There is no systematic pattern to the cases which are missing from the Office for National Statistics data, and we believe that clerical errors such as incorrect postcoding are the main reason for the discrepancy. The strong personal links between the regional and local Perinatal Mortality Survey data co-ordinators minimise the potential for cases to be missed due to this type of error.
Around half of all late fetal deaths in our population were antepartum deaths for which no specific cause could be identified. This proportion was similar for singletons and multiples, and across all birthweight categories for singletons. Other large cohort studies report similar substantial proportions of unexplained antepartum fetal deaths.1,5,15 The rate of unexplained antepartum death in singletons in our study was around 1.2 per 1000 births, compared with 1.55 per 1000 reported by Yudkin et al.15 for births in Oxford in the early 1980s. In contrast, recent hospital-based case series, with extensive diagnostic testing, have reported that a presumptive cause of death can be assigned in the vast majority of stillbirths.16,17
These variations may result from different inclusion criteria for fetal deaths, varying autopsy rates and quality, or different conventions in defining and assigning pathological findings as the underlying explanation for death. A number of authors have attributed significant proportions of deaths, which might otherwise be classified as ‘unexplained’, to diagnoses such as intrauterine growth restriction (IUGR), infection and cord problems,5,16–18 and these merit further discussion.
Fetuses which are small for gestational age are at increased risk of antepartum death.19–21 Around 40% of otherwise unexplained antepartum deaths have been reported to be small for gestational age (below the 10th centile) when compared with fetal weight standards for term live births,18 suggesting that growth restriction may be an important factor in a significant proportion of fetal deaths currently classified as ‘unexplained’. Cause classifications used routinely in the UK do not, however, code growth-restricted fetuses separately from other unexplained antepartum deaths.1
One major difficulty is establishing a clear definition of IUGR. The diagnosis may be made on the basis of clinical features and autopsy findings, or assigned wholly on the basis of low weight for gestational age. In the latter case, small for gestational age fetuses may be defined in relation to estimated fetal weight standards22 or birthweight standards.23 There is a need to identify which of these methods is the most practicable for the routine surveillance of trends in deaths associated with IUGR. The underlying aetiologies of this process, and the value of interventions such as serial growth monitoring and early delivery, also merit further investigation.
Fetal deaths attributed to infections were rare in our population, although mortality attributed to infection increased significantly over time. The most commonly identified organism was group B streptococcus; however, no deaths due to this organism were reported prior to 1988. Increased awareness of the significance of this organism as a potential cause of perinatal mortality is likely to have resulted in increased reporting in recent years in our population.24
In contrast, Peterssen et al.16 attributed 24% of fetal deaths occurring at 22 weeks of gestation or greater to infection, most commonly group B streptococcus. Studies investigating the role of amniotic fluid infection in fetal death report a substantial incidence of chorioamnionitis, suggestive of ascending infection, in live births, although lower than seen in stillbirths.25,26 This suggests that over-diagnosis is a risk, and that clear case definitions are required to monitor the true contribution of infection as a cause of fetal death.
In our population, antepartum deaths attributed to cord compression were rare, but increased over time. In a recent study, 9% of fetal deaths were attributed to ‘cord problems’.16 The significance of many cord ‘abnormalities’ in fetal death remains unclear: one large cohort study found a high prevalence of cord loops in pregnancies resulting in live birth, and no increased risk of stillbirth in such pregnancies.19
The proportion of late antepartum fetal deaths, which remain genuinely ‘unexplained’, is therefore uncertain; the contributions of growth restriction and undiagnosed infection, in particular, merit further investigation. Nevertheless, there remains a substantial group of deaths which occur unexpectedly, often close to term, in fetuses showing no evidence of growth restriction or any other abnormality. The factors leading to these deaths remain unclear, although associations have been reported with increased maternal age and with increased maternal pre-pregnancy weight.19,27,28
The most notable trend over the study period was the absence of any reduction in the rate of unexplained antepartum fetal death in singletons. Although some authors report that autopsy reduces the number of deaths which are classified as unexplained,11 in our study, unexplained antepartum deaths had a higher than average autopsy rate. It is unlikely therefore that the absence of decline in unexplained deaths can be attributed to changes in the assignment of cause of death over the study period. The stability of unexplained antepartum death rates is in notable contrast to the substantial improvement in unexplained intrapartum death rates, and suggests that modern antenatal practice is failing to impact on these deaths in our population.
Improvements in unexplained antepartum deaths were observed for some groups: multiple births and singletons with birthweights of less than 1500 g. It is possible that the underlying causes of ‘unexplained’ fetal deaths differ in these groups. A further possibility is that focussed antenatal care, involving more intensive monitoring and early delivery of these higher risk pregnancies, may have resulted in fewer antepartum deaths,29 although these deaths may be deferred rather than prevented.30 This observation, together with evidence from other settings of secular declines in unexplained antepartum stillbirth,5 suggest potential for improvement. The development of effective preventive measures, however, ultimately depends on progress in understanding the underlying aetiologies of these deaths.
The decline in the overall late fetal death rate can be attributed to reductions across a number of specific cause categories, in particular, intrapartum-related deaths, congenital anomalies, antepartum haemorrhage and pre-eclampsia. Intrapartum-related deaths reduced dramatically in all sub-groups examined. Over recent decades, intrapartum care has changed substantially, with increasing rates of operative delivery3,6 and organisational changes such as increased consultant presence on the labour ward.31 While the reduction in intrapartum-related deaths is encouraging, caution should be exercised in attributing this to any specific factors in the delivery of intrapartum care.
Late fetal deaths due to congenital anomalies also declined significantly. Over the past two decades, the use of ultrasound screening and other techniques for identifying congenital anomalies has become widespread, and termination of pregnancy is likely to have contributed to the observed reduction in late fetal deaths. In addition, the underlying prevalence of some anomalies, such as neural tube defects, has reduced,32 although chromosomal abnormalities are increasing as a result of rising maternal age.33 We found no reduction in mortality due to congenital anomalies in multiple births, which may reflect differences in screening uptake, sensitivity and outcome, and the complexity of the decision-making process with one affected and one unaffected twin.
There were few specific causes of death which did not show significant improvement over time. For several of these, such as deaths due to infection, antepartum deaths due to cord compression and deaths due to fetal blood loss, the absence of any decline is likely to reflect, at least in part, increased ascertainment over the study period.