Based on data retrieved from the NMMSS, our study found that 86.1% of maternal deaths in China between 1996 and 2005 were preventable. Both the proportion and the MMR of preventable deaths differed by regions: underdeveloped, remote areas had higher MMRs than developed, coastal regions; rural areas had higher MMRs than urban areas; and remote rural areas had the highest MMRs. The factors associated with preventable death also had regional variations, which might explain the regional disparities in PMMR. The epidemiological features of preventable maternal mortality in China have not been described in detail; hence, our findings will be of great value to the government's intervention in reducing maternal deaths.
MMR has been used as one of the key indicators evaluating the socioeconomic development of a country/region. The risk factors related to maternal deaths are usually controlled with interventions or environment improvement, which means that the reduction of MMR is, in essence, that of preventable maternal mortality. Therefore, the PMMR of a country/region reflects both the quality of its obstetric services and the quality of life of the women there. Many reports show that the proportion of maternal deaths that are preventable varies worldwide, namely, 37% in Japan, 40% in the United States , 44.4% in South Australia, 70.2% in Nigeria, and as high as 90% in Brazil. Our study indicated that the proportion of preventable maternal deaths in China between 1996 and 2005 was compatible with those in developing countries.
Although the MMR in coastal regions, inner lands and remote areas all declined during the 1996-2005 period, significant disparities were observed in urban/rural areas and by geographic locations. The PMMRs in remote and inlands areas were four and more than two times as high as that of coastal regions, respectively. It is noteworthy that the RR in inner lands was higher during the 2001-2005 period than during the 1996-2000 period. This suggests that the gap between inland and coastal regions in preventable maternal mortality might have been widening. Despite the high-speed economic growth in the past two decades, the country has seen an increasing disequilibrium in regional development. Official data released in 2005 on national economic growth showed that the average income per capita for coastal regions was 1.5 and 1.7 times higher than that for inner lands and remote areas, respectively, and was 3.5 times higher for urban areas than for rural areas. The differences were noticeably larger than that in 1996 . Remote areas have lagged behind in economic development, but favourable state policies and health projects have enabled them to improve the health of local women and children by a larger margin and at a higher speed than inner lands . By contrast, inner lands experienced a "bottleneck" in economic and medical undertakings because they did not have the economic advantages of the coastal regions or the favourable policies and projects of the remote areas. This situation was best reflected by the large difference in PMMR and relatively stable RR during different periods. In remote areas, the marked reduction in PMMR and minimization of RR during different periods further proved that special intervention programs such as "Reducing Maternal Mortality and Eliminating Newborn Tetanus" by the government achieved a good result.
The cause-specific PMMR also presented regional differences in China during 1996-2005. Obstetric haemorrhage was the leading cause of maternal mortality across the country but comprised different proportions of the preventable cause-specific deaths; it was most prevalent in remote areas, followed by inner lands and coastal regions. As medical sciences advance, 90% of obstetric haemorrhage should be preventable when sufficient blood supply, easy transport, and skilful medical procedures are available . Although the proportion of deaths due to obstetric haemorrhage increased in coastal regions during the 2001-2005 period, the MMR still remained the lowest among the three regions. In the United States and Europe, maternal deaths due to obstetric haemorrhage have been reduced to an extremely low level, and haemorrhage has been replaced by embolism, cardiac disorders, and other unavoidable factors as the leading cause of maternal mortality . However, in developing countries such as China, the largest proportion of maternal deaths still results from obstetric haemorrhage. According to a WHO estimate, obstetric haemorrhage accounted for 30.8% of all maternal deaths among Asian women . The situation is becoming worse in China, particularly in remote areas where women have the highest risk of dying from obstetric haemorrhage. Although there was a decreasing trend in other cause-specific PMMRs besides obstetric haemorrhage, regional gaps in the PMMR were still obvious. Women in remote and inland areas had a higher risk of dying from pregnancy-induced hypertension, cardiac disorders, and puerperal infection than those in coastal regions. To some extent, the reduction of MMR in China depends on the reduction of deaths due to these conditions.
It has been widely accepted that MMR in a specified area is affected by socioeconomic status in addition to the development of healthcare systems. In China, 80% of health resources were concentrated in big cities , and 80% of these resources were concentrated in large urban hospitals . There were more abundant healthcare resources and human resources in coastal regions, and the number of technicians (with bachelor degrees and senior professional titles) was much higher than in inland and remote regions. In terms of types of obstetric services, such as caesarean section, hysterectomy and blood transfusion, there were no large differences between health institutions at the county level and provincial level. However, grassroots health institutions in rural and remote regions had the lowest obstetric service quality due to the inadequate medical facilities and obstetrician skill [34, 35]. Undoubtedly, the coastal region of China has a well-developed socioeconomic and healthcare system. If effective measures are taken, the maternal healthcare in the inland and remote areas can achieve the same level.
Our findings reveal that the factors associated with maternal mortality also differed by region. Knowledge/skill of individual/family seemed to be the major factor for remote areas, where women or their families were usually under-educated or ill-informed, resulting in ignorance of pregnancy/delivery-related risks, absence of prenatal examination, or inability to identify risks of pregnancy-related complications. Most of these women underwent home delivery attended by inadequately trained family members or relatives . As they were undereducated, elderly and slow at learning new knowledge, most midwives could not properly handle obstetric complications during delivery, such as retention of the placenta and uterine inertia, which may lead to maternal death at home or on the way to the hospital. In 2005, the hospital delivery rates in rural and remote areas were 76.22% and 33.20%, respectively, which is far lower than that in urban areas (95%) . However, in coastal regions that enjoyed developed economies, rich health resources, easy transport and high accessibility of health services, most women preferred hospital delivery. The insufficient knowledge/skills of the health professionals became the major factor. The deaths happened mainly in medical institutions at the township and county level and usually resulted from such conditions such as delay in identifying or handling problems or risks during pregnancy, delivery, or puerperium; ignorance of proper referral for certain diseases; and poor surgical skills. Interestingly, remote areas had fewer problems than coastal regions concerning the knowledge/skills of health professionals, which was probably due to fewer hospital visits of the women in remote areas where health resources were scarce and access to obstetric services was inconvenient. The large proportion of maternal deaths due to individual/family factors may mask the significance of the knowledge/skills of medical institutions in remote areas. Thus, for the Chinese government, it is important to improve the knowledge/skills of individuals/families and health professionals in medical institutions, irrespective of where they live.
In summary, there are great regional disparities in preventable maternal mortality and associated factors. The decreasing trends observed in the overall PMMRs and cause-specific PMMRs suggest that the MMR in rural and inland regions can be reduced remarkably if effective measures are taken. Improvements in the economy or healthcare will be of great benefit to control or diminish environmental factors associated with preventable deaths, eventually minimizing MMR and the regional gaps within China. These findings also indicate that maternal mortality in a developing country/region will be reduced substantially if its economy, culture and healthcare are improved.
Our study has some limitations: (1) The early abortion-related maternal deaths outside the hospital were likely to be underreported, especially in the regions with a weak maternal and child healthcare system, although NMMSS covers the entire period of pregnancy and has unified quality control measures. (2) Direct analysis of the relationship between maternal death and prenatal healthcare was not possible because the detailed perinatal healthcare data for individual deaths were not collected. Many studies have shown that maternal death is associated with several social factors besides healthcare service quality [19, 38]. Scholars have been aware of the large rural-urban difference and regional difference in maternal death for a long time; however, appropriate data to explore the cause of the difference cannot be found. This paper used the large population-based surveillance data, and therefore, the results were reliable, which was of great value for adopting effective measures to reduce maternal death in developing countries where developed, developing and underdeveloped regions coexisted.