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1.
OBJECTIVE: To report stillbirth and early neonatal mortality and to quantify the relative importance of different primary obstetric causes of perinatal mortality in 171 perinatal deaths from 7993 pregnancies that ended after 28 weeks in nulliparous women. METHODS: A review of all stillbirths and early newborn deaths reported in the WHO calcium supplementation trial for the prevention of pre-eclampsia conducted at seven WHO collaborating centres in Argentina, Egypt, India, Peru, South Africa and Viet Nam. We used the Baird-Pattinson system to assign primary obstetric causes of death and classified causes of early neonatal death using the International classification of diseases and related health problems, Tenth revision (ICD-10). FINDINGS: Stillbirth rate was 12.5 per 1000 births and early neonatal mortality rate was 9.0 per 1000 live births. Spontaneous preterm delivery and hypertensive disorders were the most common obstetric events leading to perinatal deaths (28.7% and 23.6%, respectively). Prematurity was the main cause of early neonatal deaths (62%). CONCLUSIONS: Advancements in the care of premature infants and prevention of spontaneous preterm labour and hypertensive disorders of pregnancy could lead to a substantial decrease in perinatal mortality in hospital settings in developing countries.  相似文献   

2.
The relation between long-term temporal trends in stillbirth and neonatal death rates and the congenital malformation frequencies in such deaths were analysed, using data from hospital-based European, USA, and Canadian reports published from 1950. In the last 50 years the overall perinatal mortality rate has fairly steadily improved, decreasing by 65-80%. This was accomplished by the control of some serious problems of early life. However, lingering disorders form an ever larger proportion of the causes of perinatal mortality. Among the prominent of these are congenital malformations, accounting for nearly 30% of perinatal deaths at present. However, this figure conceals important differences between stillbirths and early neonatal deaths. For example, although stillbirth and early neonatal mortality rates have decreased to similar extents during these years, congenital malformations, which were almost equally frequent causes of death in both of them at the beginning of this period, are now about twice as common in early neonatal (one week) deaths as in stillbirths. Other differences between them are in birthweight-related malformation frequencies and in characteristic arrays of malformations. The significance of these patterns and of some geographical variations, and the likelihood of continuing improvement in the stillbirth and early neonatal mortality rates are discussed.  相似文献   

3.
Since the midtwentieth century, stillbirths (late fetal deaths) and early neonatal deaths have often been combined into a single category of "perinatal" deaths. In the past, such a combination was justified by the fact that asphyxia was a common cause of death during labor (intrapartum stillbirth) and shortly after birth and by geographic and temporal differences in classification of livebirths versus stillbirths. In more recent years, however, the etiologic determinants have diverged sharply, with many fewer early neonatal deaths caused by asphyxia and relatively many more caused by congenital anomalies. Moreover, the increasingly common stratification of pregnancy outcome measures by gestational age or birth weight leads to the use of an inappropriate denominator (total livebirths plus stillbirths within each gestational age or birth weight category) for denoting risk for the stillbirth component, because all unborn fetuses (including the majority of those not born within the specified gestational age or birth weight range) are at risk of being stillborn in that range. The authors suggest that, whenever possible, stillbirths and early neonatal deaths should be reported separately, with gestational age-specific risks of stillbirth based on all fetuses at risk, and that antepartum and intrapartum stillbirths be reported separately.  相似文献   

4.
Each year, an estimated six million perinatal deaths occur worldwide, and 98% of these deaths occur in low- and middle-income countries. These estimates are based on surveys in both urban and rural areas, and they may underrepresent the problem in rural areas. This study was conducted to quantify perinatal mortality, to identify the associated risk factors, and to determine the most common causes of early neonatal death in a rural area of the Democratic Republic of the Congo (DRC). Data were collected on 1,892 births. Risk factors associated with perinatal deaths were identified using multivariate analysis with logistic regression models. Causes of early neonatal deaths were determined by physician-review of information describing death. The perinatal mortality rate was 61 per 1,000 births; the stillbirth rate was 30 per 1,000 births; and the early neonatal death rate was 32 per 1,000 livebirths. Clinically-relevant factors independently associated with perinatal death included: low birthweight [odds ratio (OR)=13.51, 95% confidence interval (CI) 7.82-23.35], breech presentation (OR)=12.41; 95% CI 4.62-33.33), lack of prenatal care (OR=2.70, 95% CI 1.81-4.02), and parity greater than 4 (OR=1.93 95% CI 1.11-3.37). Over one-half of early neonatal deaths (n=37) occurred during the first two postnatal days, and the most common causes were low birthweight/prematurity (47%), asphyxia (34%), and infection (8%). The high perinatal mortality rate in rural communities in the DRC, approximately one-half of which is attributable to early neonatal death, may be modifiable. Specifically, deaths due to breech presentation, the second most common risk factor, may be reduced by making available emergency obstetric care. Most neonatal deaths occur soon after birth, and nearly three-quarters are caused by low birthweight/prematurity or asphyxia. Neonatal mortality might be reduced by targeting interventions to improve neonatal resuscitation and care of larger preterm infants.  相似文献   

5.
Maternal obesity is associated with impaired fetal and neonatal survival, but underlying mechanisms are poorly understood. We examined how prepregnancy BMI and early gestational weight gain (GWG) were associated with cause-specific stillbirth and neonatal death. In 85,822 pregnancies in the Danish National Birth Cohort (1996–2002), we identified causes of death from medical records for 272 late stillbirths and 228 neonatal deaths. Prepregnancy BMI and early GWG derived from an early pregnancy interview and Cox regression were used to estimate associations with stillbirth or neonatal death as a combined outcome and nine specific cause-of-death categories. Compared to women with normal weight, risk of stillbirth or neonatal death was increased by 66% with overweight and 78% with obesity. Especially deaths due to placental dysfunction, umbilical cord complications, intrapartum events, and infections were increased in women with obesity. More stillbirths and neonatal deaths were observed in women with BMI < 25 and low GWG. Additionally, unexplained intrauterine death was increased with low GWG, while more early stillbirths were seen with both low and high GWG. In conclusion, causes of death that relate to vascular and metabolic disturbances were increased in women with obesity. Low early GWG in women of normal weight deserves more clinical attention.  相似文献   

6.
This study evaluated the diagnostic accuracy of a verbal autopsy (VA) tool in ascertaining the causes of stillbirths and neonatal deaths in rural Ghana and was nested within a community-based maternal vitamin A supplementation trial (ObaapaVitA trial). All stillbirths and neonatal deaths between 1 January 2003 and 30 June 2004 were prospectively included. Community VAs were carried out within 6 months of death and were classified with a primary cause of death by three experienced paediatricans. The reference standard diagnosis was obtained by the study paediatrician in 4 district hospitals in the study area.
There were 20 317 deliveries, 661 stillbirths and 590 neonatal deaths with a VA diagnosis in the study population. A total of 311 stillbirths and 191 neonatal deaths had both a VA and a hospital reference standard diagnosis. The VA performed poorly for stillbirth diagnoses such as congenital abnormalities and maternal haemorrhage. Accuracy was higher for intrapartum obstetric complications and antepartum maternal disease. For neonatal deaths, sensitivity was >60% for all major causes; specificity was 76% for birth asphyxia but >85% for prematurity and infection. Overall, VA diagnostic accuracy was higher than expected in this rural African setting. Our classification system was based on the expected public health importance of the individual causes of death, differing implications for intervention and the ability to distinguish between the individual causes in low-resource settings. We believe this system was easier to use than traditional approaches and resulted in high precision and accuracy. However, further simplifications are needed to allow use of the World Health Organisation VA in routine child health programmes. The diagnostic accuracy of the VA tool should also be assessed in other regions and in multicentre studies.  相似文献   

7.
Perinatal mortality refers to stillbirths and deaths which occur during the first week of life. 7 million such deaths occur annually worldwide, almost all of which are in developing countries. Rates as high as 75-100 deaths/1000 births have been documented in developing countries. The 3 leading causes of perinatal mortality are complications of pre-term birth, birth asphyxia and birth trauma, and bacterial infections. The other causes of perinatal mortality are largely unknown due to difficulties in documenting stillbirths in developing countries. In many developing country societies, it is culturally unacceptable to acknowledge a birth until it has survived its first week of life. This study identified and quantified the risk factors for perinatal deaths in a rural community in Manikganj district, Bangladesh. Cases were mothers whose infants died in the perinatal period, while comparison mothers were those whose infants survived the perinatal period. Of the 186 infant deaths recorded, 130 (69.9%) were in the perinatal period, and included 53 stillbirths. The perinatal death rate was 64.5/1000 births. Logistic regression confirmed that maternal age, parity, and mal-presentation were significantly associated with perinatal deaths. Mal-presentation was independently associated with a increased risk of perinatal death.  相似文献   

8.
We describe a prospective cross-sectional survey over a 12-month period in the principal maternity hospital of Kathmandu, Nepal, where over 50% of the local population deliver. The study aim was to estimate the contribution of birth asphyxia to perinatal mortality in this setting. During 1995, there were 14,371 livebirths and 400 stillbirths, a total stillbirth rate of 27 per 1000 total births. The fresh term (2000 g or more) stillbirth rate was 8.5 per 1000 total births [95% CI 7.1, 10.1]. Ninety-two cases of neonatal encephalopathy (NE) affecting term infants were detected (excluding those due to congenital malformations, hypoglycaemia and early neonatal sepsis). The birth prevalence of NE was 6.4 per 1000 livebirths [95% CI 5.2, 7.8]. There was evidence of intrapartum compromise in 63 (68%) of the cases of NE and 65 (76%) of the stillbirths, but only in 12 (12%) of controls. The cause-specific early neonatal mortality rate for NE was 2.1 per 1000 livebirths [95% CI 1.4, 3.0]. Combining the NE deaths and fresh stillbirths gives an upper estimate for term birth asphyxia perinatal mortality rate of 10.8 per 1000 total births [95% CI 9.2, 12.6], 24% of all perinatal deaths before hospital discharge. This study suggests that birth asphyxia remains an important cause of perinatal mortality in developing countries. The paper discusses the pros and cons of different strategies to reduce birth asphyxia in low-income countries.  相似文献   

9.
Obstetric complications and newborn illnesses amenable to basic medical interventions underlie most perinatal deaths. Yet, despite good access to maternal and newborn care in many transitional countries, perinatal mortality is often not monitored in these settings. The present study identified risk factors for perinatal death and the level and causes of stillbirths and neonatal deaths in the West Bank and Gaza Strip. Baseline and follow-up censuses with prospective monitoring of pregnant women and newborns from September 2001 to August 2002 were conducted in 83 randomly selected clusters of 300 households each. A total of 113 of 116 married women 15-49 years old with a stillbirth or neonatal death and 813 randomly selected women with a surviving neonate were interviewed, and obstetric and newborn care records of women with a stillbirth or neonatal death were abstracted. The perinatal and neonatal mortality rates, respectively, were 21.2 [95% confidence interval (CI) 16.5, 25.9] and 14.7 [95% CI 10.2, 19.2] per 1000 livebirths. The most common cause (27%) of 96 perinatal deaths was asphyxia alone (21) or with neonatal sepsis (5), while 18/49 (37%) early and 9/19 (47%) late neonatal deaths were from respiratory distress syndrome (12) or sepsis (9) alone or together (6). Constraint in care seeking, mainly by an Israeli checkpoint, occurred in 8% and 10%, respectively, of 112 pregnancies and labours and 31% of 16 neonates prior to perinatal or late neonatal death. Poor quality care for a complication associated with the death was identified among 40% and 20%, respectively, of 112 pregnancies and labour/deliveries and 43% of 68 neonates. (Correction added after online publication 5 June 2008: The denominators 112 pregnancies, labours, and labour/deliveries, and 16 and 68 neonates were included; and 9% of labours was corrected to 10%.) Risk factors for perinatal death as assessed by multivariable logistic regression included preterm delivery (odds ratio [OR] = 11.9, [95% CI 6.7, 21.2]), antepartum haemorrhage (OR = 5.6, [95% CI 1.5, 20.9]), any severe pregnancy complication (OR = 3.4, [95% CI 1.8, 6.6]), term delivery in a government hospital and having a labour and delivery complication (OR = 3.8, [95% CI 1.2, 12.0]), more than one delivery complication (OR = 4.4, [95% CI 1.8, 10.5]), mother's age >35 years (OR = 2.9, [95% CI 1.3, 6.8]) and primiparity in a full-term pregnancy (OR = 2.6, [1.1, 6.3]). Stillbirths are not officially reportable in the West Bank and Gaza Strip and this is the first time that perinatal mortality has been examined. Interventions to lower stillbirths and neonatal deaths should focus on improving the quality of medical care for important obstetric complications and newborn illnesses. Other transitional countries can draw lessons for their health care systems from these findings.  相似文献   

10.

Background

Perinatal mortality is reported to be five times higher in developing than in developed nations. Little is known about the commonly associated risk factors for perinatal mortality in Southern Nations National Regional State of Ethiopia.

Methods

A case control study for perinatal mortality was conducted in University hospital between 2008 and 2010. Cases were stillbirths and early neonatal deaths. Controls were those live newborns till discharged from the hospital. Subgroup binary logistic regression analyses were done to identify associated risk factors for perinatal mortality, stillbirths and early neonatal deaths.

Results

A total of 1356 newborns (452 cases and 904 controls) were included in this analysis. The adjusted perinatal mortality rate was 85/1000 total delivery. Stillbirths accounted for 87% of total perinatal mortality. The proportion of hospital perinatal deaths was 26%. Obstructed labor was responsible for more than one third of perinatal deaths. Adjusted odds ratios revealed that obstructed labor, malpresentation, preterm birth, antepartum hemmorrhage and hypertensive disorders of pregnancy were independent predictors for high perinatal mortality. In the subgroup analysis, among others, obstructed labor and antepartum hemorrhage found to have independent association with both stillbirths and early neonatal deaths.

Conclusion

The perinatal mortality rate was more than two fold higher than the estimated national perinatal mortality;and obstructed labor, malpresentation, preterm birth, antepartum hemmorrhage and hypertensive disorders of pregnancy were independent predictors. The reason for the poor progress of labor and developing obstructed labor is an area of further investigation.  相似文献   

11.
12.
2005~2008年上海市围产儿死亡情况分析   总被引:2,自引:2,他引:0  
朱丽萍  许厚琴  秦敏  李芬  金辉 《中国妇幼保健》2009,24(34):4844-4846
目的:通过对上海市2005~2008年围产儿死亡情况分析,了解上海市围产儿死亡及其评审工作的现状,为探索进一步降低围产儿死亡率及健全围产儿死亡评审制度提供依据。方法:回顾性分析2005~2008年上海市围产儿全部死亡个案及评审资料。结果:①上海市围产儿死亡率5.38‰,其中本市户籍2.95‰,非本市户籍73.00‰。②围产儿死亡中死胎、死产、早期新生儿死亡的构成比分别为61.88%、7.92%和30.20%,死胎构成比保持在61.00%,死胎构成比较稳定,死产构成比从2005年的9.08%下降到2008年的7.06%,早期新生儿死亡构成比从2005年的29.18%上升到2008年的31.90%。除了本市户籍者中早期新生儿死亡率略有上升外,死胎、死产的发生率均有明显下降。③前5位死因顺位依次为不明原因、严重畸形、优生引产、胎盘早剥和早产儿。④评审结果:区级评审的围产儿死亡中Ⅰ、Ⅱ类死亡者占16.66%,而早期新生儿死亡中的Ⅰ、Ⅱ类死亡占26.25%。区级评审有争议的典型案例经过市级复评审,结果升级的占50.60%。结论:进一步降低围产儿死亡率,需要加强出生缺陷一、二级预防和提高新生儿抢救能力,此外需要规范和提高围产儿死亡评审的质量。  相似文献   

13.
Wang PD  Lin RS 《Public health》1999,113(1):27-33
Information on perinatal deaths was obtained from 310 women by collecting detailed obstetric histories dating from marriage to the start of the survey. These histories were compared to those of 688 age matched controls. Potential risk factors, levels and time trends of perinatal mortality in Taiwan were examined and factors underlying stillbirths and early neonatal deaths were also compared using conditional logistic regression analyses. A nearly 56% decline of the perinatal mortality rate during the 35 y, approximately, prior to the survey was observed. Risk of stillbirths was increased among those who had abused illegal drugs during pregnancy, those who reported that the pregnancy was unwanted and those with Thalassemia trait. Body mass index was log-linearly related with stillbirths, with higher body mass associated with higher risk. For early neonatal deaths, those mothers aged 19 y or less, those giving birth to either their first children or to their fifth or later child, those who had their first prenatal care visit after the first three months of pregnancy were associated with increased risk in the logistic model. Those with a birth interval of less than two years and those with less education were associated with increased risk in both perinatal death groups. While some of these factors have already been associated with perinatal deaths, others have not; the new associations provide clues to mechanisms by which the risk of death increases before or after delivery.  相似文献   

14.
Fetal deaths account for nearly one percent of all births in the United States. The cost of hospital care associated with fetal deaths may be substantial. However, there is very limited data on the economic burden of fetal death. We conducted a retrospective medical chart review of stillbirths at three large hospitals in Michigan over a ten-year period and identified medical complications, hospital costs, and length of stay for these deliveries. Mothers with stillbirth were matched with mothers of the same age who delivered a live-born infant at the same hospital during the same year. Our final sample was comprised of 533 stillbirths and 1,053 matched live births. Average hospital cost for stillbirth was $7,495 (±7,015) and the average length of stay was 2.8 days (±2.8). Having a serious maternal medical complication was associated with higher costs and longer length of stay among women with stillbirth. Early stillbirths between 20 and 28 weeks gestational age, epidural/spinal/general anesthesia, and cesarean delivery were also associated with longer length of stay. Average hospital costs for women with stillbirth were more than $750 higher than women with live births but length of stay was not significantly different between the two. This study suggests that stillbirths were associated with substantial maternal hospital costs. Future research examining the economic impact of stillbirths beyond labor and delivery such as increased costs associated with additional testing and care in subsequent pregnancies will help better understand the overall economic impact of stillbirths.  相似文献   

15.
Summary. Epidemiological data derived from death certification in the absence of a necropsy can be erroneous. Despite concern over adult hospital necropsy rates, which have fallen dramatically in the last 40 years, relatively less has been published regarding perinatal necropsy rates. A literature review of necropsy rates for neonatal deaths, stillbirths and perinatal losses was undertaken. There is a wide variation in the perinatal necropsy rates worldwide but the numbers appear to be higher than adult hospital rates. The necropsy rate for neonatal deaths appears to be lower than that for stillbirths. It is hoped that the review will serve to alert readers to remain vigilant against any fall in the perinatal necropsy rates.  相似文献   

16.
Levels and risk factors for perinatal mortality in Ahmedabad, India   总被引:4,自引:0,他引:4  
To estimate levels and determinants of perinatal mortality, we conducted a hospital-based surveillance and case-control study, linked with a population survey, in Ahmedabad, India. The perinatal mortality rate was 79.0 per 1000, and was highest for preterm low-birth-weight babies. The case-control study of 451 stillbirths, 160 early neonatal deaths and 1465 controls showed that poor maternal nutritional status, absence of antenatal care, and complications during labour were independently associated with substantially increased risks of perinatal death. Multivariate analyses indicate that socioeconomic factors largely operate through these proximate factors and do not have an independent effect. Estimates of attributable risk derived from the prevalence of exposures in the population survey suggest that improvements in maternal nutrition and antenatal and intrapartum care could result in marked reductions of perinatal mortality.  相似文献   

17.
OBJECTIVE: To assess the rates, timing and causes of neonatal deaths and the burden of stillbirths in rural Uttar Pradesh, India. We discuss the implications of our findings for neonatal interventions. METHODS: We used verbal autopsy interviews to investigate 1048 neonatal deaths and stillbirths. FINDINGS: There were 430 stillbirths reported, comprising 41% of all deaths in the sample. Of the 618 live births, 32% deaths were on the day of birth, 50% occurred during the first 3 days of life and 71% were during the first week. The primary causes of death on the first day of life (i.e. day 0) were birth asphyxia or injury (31%) and preterm birth (26%). During days 1-6, the most frequent causes of death were preterm birth (30%) and sepsis or pneumonia (25%). Half of all deaths caused by sepsis or pneumonia occurred during the first week of life. The proportion of deaths attributed to sepsis or pneumonia increased to 45% and 36% during days 7-13 and 14-27, respectively. CONCLUSION: Stillbirths and deaths on the day of birth represent a large proportion of perinatal and neonatal deaths, highlighting an urgent need to improve coverage with skilled birth attendants and to ensure access to emergency obstetric care. Health interventions to improve essential neonatal care and care-seeking behavior are also needed, particularly for preterm neonates in the early postnatal period.  相似文献   

18.
Perinatal deaths     
《Africa health》1995,17(5):26-27
Although the perinatal mortality rate (PNMR) has long been used in developed countries as a measure of the health and quality of the services in a community, it is less clearly related to other health indicators in developing countries. This is because a high perinatal loss is often accepted fatalistically and because data are incomplete. A 1995 report from a rural hospital and its related community in Zululand analyzed the component of PNM that could be regarded as avoidable in the local circumstances. The definition used was a stillbirth or death in the first 7 days of life, occurring after 28 weeks of gestation. The study included every perinatal death over a 2-year period. In that time there were 280 perinatal deaths in 8237 deliveries, giving a rate of 34/1000. All deliveries in the rural hospital and the 7 associated outlying clinics and those occurring before admission were included, and this covered more than half of the births in the locality. There were 10% more births in the 2nd year of the study and 30% more perinatal deaths in the 2nd year. This was attributed to the attraction of more high-risk cases because of improved facilities. Overall, in the 2-year period, 9.6% of the deaths were classified as avoidable, falling from 19% in the first 6 months to 3% in the last 6 months. This reduction of avoidable deaths was attributed to certain types of intervention: 1) Reorganization of services and the provision of a high-risk clinic with advanced training for some midwives and better continuity of medical staff. 2) A basic set of management guidelines, especially for referral from outlying clinics to hospital. In-service education provided an important reinforcement. 3) Continuous perinatal audit. Progress and the figures were shared with staff regularly. Confidential updates were provided to outlying clinics monthly to maintain interest and motivation.  相似文献   

19.
Objectives An enhanced surveillance system that integrated health information systems and extended surveillance to previously uncovered areas to capture all births, perinatal and maternal deaths in a rural district of Pakistan was established in 2015, and this study uses capture–recapture methodology to assess completeness. Methods Births and deaths collected by the survey were matched with the data captured by the enhanced surveillance system. Capture–recapture methodology was used to estimate the total number of births and deaths, measure the degree of underestimation, and adjust mortality rates. Results Of all births, 99% were captured by the enhanced surveillance system. Ninety percent of neonatal deaths and 86% of early neonatal deaths were recorded. The recorded neonatal mortality rate was 40 per 1000 live births (95% CI 35–44), and after adjustment for under-enumeration was 42 per 1000 live births (95% CI 37–46). Recorded rates underestimated neonatal mortality by 5% and perinatal mortality by 7%. Five stillbirths were recorded by the survey and all were matched to recorded stillbirths. The one maternal death recorded by the survey was matched with the maternal death captured by the enhanced surveillance system. The maternal mortality ratio prior to adjustment for under-enumeration was 247 per 100,000 live births (95% CI 147–391), whereas after adjustment it was 246 per 100,000 live births (95% CI 146–389). Conclusion Application of capture–recapture methods to the enhanced surveillance system indicated a high completeness of birth and death recording by the surveillance system.  相似文献   

20.
There has been a trend over the past two decades in some Western countries for women to delay childbearing, a factor associated with an increased risk of perinatal mortality (stillbirth and neonatal death). While the rates of stillbirth and neonatal mortality have improved in some countries, it has not been established whether maternal age remains a risk factor for perinatal mortality in Australia. The Western Australian Maternal and Child Health Research Database (MCHRDB) was used to examine the effect of maternal age on perinatal death in the periods 1984-93 and 1994-2003 after adjustment for parity and sociodemographic factors. Stillbirths and neonatal deaths were analysed separately. The crude rate of stillbirth has shown little change over the 20 years examined remaining at around 7.5 per 1000 total births, while the rate of neonatal death has decreased steadily from 5.4 per 1000 livebirths in 1984 to 2.0 in 2003. Older maternal age remains a risk factor for stillbirth but the relative risk has declined. After adjustment for parity and sociodemographic factors the relative risk of stillbirth for a woman aged over 40 years (compared with a woman aged 25-29 years) decreased from 2.6 in the period 1984-93, to 1.9 in the period 1994-2003. The increased risk of stillbirth associated with teenage mothers was fully explained by sociodemographic factors in both time periods. No increased risk of neonatal death was evident in the recent period 1994-2003 for teenage or older mothers after adjustment for parity and sociodemographic factors. In spite of some improvements over the past 20 years, women 30 years of age and older continue to be at increased risk of stillbirth. The risk of neonatal death is no longer associated with increased maternal age; however, the small number of cases in the older maternal age groups may be a result of the increased prevalence of antenatal screening and terminations for birth defects.  相似文献   

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