This study was a population-based surveillance for APOs in Shanxi Province in northern China. To the best of our knowledge, this study is the first report on the APOs prevalence and epidemiology in Shanxi Province of northern China. Firstly, we found that birth prevalence of premature births, LBW and macrosomia was extremely high among all APOs, with macrosomia showing an obvious upward trend from 2007 to 2012. While birth prevalence of birth defects, neonatal deaths and stillbirths stayed around at a relatively low level. For years, the whole nation has provided large sum of financial support in researches on birth defects, stillbirths and neonatal deaths and established a complete and effective 3-Level Prevention System (namely, the primary, secondary and tertiary health network). Achievements were world-recognized, as China has seen dramatic reductions in infant and child mortalities particularly in the past 15 years and in incidence rate of major birth defects from 2.74‰ (1987) to 0.15‰ (2017), a 94.5% decline[21, 22].
China has made remarkable achievements in prevention and intervention of birth defects for the past 30 years. With the social, economic and nutritional improvement, the constituent of APOs has changed in recent years. The infant mortality caused by birth defects, stillbirths and neonatal deaths declined, while the prevalence of children’s chronic diseases relevant to prematurity, LBW and macrosomia surged. Currently, population policy in China still gives large financial support for birth defects research. By contrast, the other three APOs have been relatively neglected (like macrosomia) or received insufficient attention (like prematurity and LBW). Investment in prevention and community coverage is far from enough. There exists a clear knowledge gap for prematurity in China, and research into its burden, determinants, and effects is urgently needed[23]; in some places, macrosomia is not even taken as a problem by their families. Yet their unfavorable consequences might be huge and nonnegligible and continuing for lifelong. Lots of studies have shown that preterm births are under greater risks of neurodevelopmental impairments (such as mental retardation and cerebral palsy), behavioral sequelae (such as dysfunction in cognitive areas) and other problems like hospital readmissions[24]; LBW newborns are at an increased risk of the development of coronary heart disease[25], depression and anxiety[26], poor long-term consequences on lung functions[6], diabetes, blood pressure and neurological functions in later life[27]; macrosomia infants are at elevated short-term risks like shoulder dystocia and long-term risks of metabolic syndrome, asthma and even cancer[28]. What’s more, prematurity-associated complications and macrosomia are proven to be closely related to neonatal deaths and both fetal growth restriction and preterm births are strongly associated with placental dysfunction and subsequent poor fetal health, carrying increased risks of stillbirths[9, 17, 23]. In another word, China can’t effectively reduce the infant mortality and incidence of chronic diseases without prevention of prematurity, LBW and macrosomia. Enough attention, investment and measures must be taken to address the three previously-neglected APOs.
The second important finding of the study was that there appeared a “U-shape” distribution of birth prevalence of five APOs (namely, prematurity, neonatal deaths, birth defects, stillbirths, LBW), as maternal age increased. For macrosomia, its prevalence rose monotonously with rising maternal ages, a phenomenon consistent in previous researches[29]. For other APOs, previous researchers have mostly agree that there exists a “nadir” maternal age where the risks of APOs are the lowest, as our study found out, but the exact age of the “nadir” hasn’t come to consistent conclusion and it seems to vary in different populations, with some finding extremes of maternal childbearing age as risk factors for APOs and taking 20–29, 25–29 or 20–35 age-group as the “nadir” and some others observing a proportionally increased risks of APOs with maternal age in African-Americans and calling it “weathering effect”[11, 27, 30]. The latter views argue that the “weathering effect” is a manifestation of worsening health status and cumulative exposure to hardship as maternal age increases[31]. In fact, it’s seen that adolescent mothers are mostly single, with low incomes, inadequate prenatal care and lower antenatal maternal weight,[32] all of which are commonly seen risk factors of APOs.
Similarly, for the older age group, it’s important to ask whether the higher risks are the results of age itself, of age accumulation of biological disadvantages such as hypertension and diabetes[27] that lead to pregnancy complications, of accumulation of unfavorable social-economic behaviors and environmental exposures like smoking and air pollution[33, 34], or of a composite or interactions of the above[33, 35]. The answer of this question is crucial for formulating public health policies and allocating public health resources in different maternal age groups. Some investigations state that the weathering effect is modified by the mother’s socio-economic situation and tends to be most pronounced in women of lower socio-economic status[33]. If it’s true, then it seems that the “weathering effect” for most APOs did be “modified” in Pinding and Xiyang County, indicating the relatively fine local maternal socio-economic situation. However, as discussed before, the underlying relationship between maternal age and APOs is complex and incompletely understood, especially in China where few literatures looked specifically into it. Our study can only serve as a clue and it calls for more well-designed studies to explore the cause-effect relations.
Thirdly, gender differences existed in birth weights, with macrosomia happening more for male fetuses and LBW more for females, a conclusion in accordance with other researches[27, 29]. This difference is thought to be generated by different androgen actions and the fact that at a given birth weight boys have younger gestational age indicates that males grow more and faster[36, 37]. It’s suggested that male fetuses are more vulnerable than their female counterparts and that male fetuses are at greater risks of death or damage from almost all the obstetric catastrophes that can happen before birth[38]. It is observed by some studies that neonatal deaths, congenital anomaly and stillbirths are commoner in boys[39]. In our cohort study, however, such gender differences were not detected.
There are some strengths in our study. It was a population-based surveillance study for APOs in Shanxi Province in northern China. It’s one of few researches to describe the overall situation of APOs in rural Shanxi Province, China, providing clues for epidemiological distribution of APOs in rural China and future analysis of causal effect of demographic factors. Our surveillance system was based on an improved 3-tier health care system, and the case ascertainment was relatively complete. The population design and higher population covering (over 95%) minimized the selection bias. In addition, all APOs were detected, coded and reviewed carefully by well-trained investigators and professional physicians in every effort to reduce possible detection bias. However, potential limitation should also be acknowledged. The surveillance system was confined to resident women, and therefore might omit some with short-term stay. Yet considering population migration was not significant in these two counties and the population design insured over 95% population covering[40], the omission wouldn’t affect the estimation of birth prevalence for the six APOs.