Toward a National Birth Cohort Study in China.

China has a strong need and strong reasons to conduct a large-scale birth cohort study. Environmental pollution is a serious problem in some parts of the country. Infertility, miscarriage, birth defects, childhood asthma, childhood obesity, and sexual prematurity have all reportedly increased in recent years, but the causes remain elusive. With fewer children in each family, child health is often the central focus of a family. Rising maternal and child morbidity raise serious public concerns. China also has great variations in geographic characteristics, nutrition, regional economy, and tradition. The uneven economic development among regions has resulted in disparities in health status and disease characteristics of the local populations. In some areas, the disease pattern is similar to that of a developed country, whereas in others it resembles that of a low-income country. Thus, a national birth cohort study in China could offer rich opportunities to study a variety of social and cultural factors, environmental exposure, and nutrition, behavior, and genetic factors in child health and development. Equally important is that China has a well-established maternal and child health (MCH) care system, with almost 100% coverage ofwomen and children. “MCH Centers,” an administrative entity for MCH, are instituted at national, provincial, city, and county levels. These centers are usually based in maternity or children’s hospitals and are responsible for all MCH programs within their administration region. This vast MCH network with a centralized administration system provides an excellent opportunity to carry out a large-scale prospective cohort study efficiently. In a word, a national birth cohort study in China is important, feasible, and affordable. China has conducted similar large-scale studies before. The China–US Collaborative Project for Neural Tube Defect Prevention contributed to the dramatic decrease in this defect by promoting folic acid supplementation in the past decades. Much smaller but more comprehensive birth cohort studies have been launched in several cities in recent years. Considering China’s population size and vast rural areas, a national birth cohort study is warranted. However, substantial challenges lie at every step in building such a cohort. It is considered ideal to have a cohort that starts before conception. China is one of the few countries in the world that have an infrastructure that facilitates preconception recruitment. The government promotes preconception care to reduce birth defects and improve pregnancy outcomes by offering free preconception care to couples nationwide who plan to initiate a pregnancy. Investigators can recruit couples at designated preconception care clinics, which are usually located in maternity hospitals. Having a preconception cohort enables us to prospectively study both male and female contributions to reproductive outcomes, early human development, and offspring health. However, a preconception cohort has drawbacks. For various reasons, some couples do not try to conceive consistently or later decide not to conceive in the near future. Thus, more women are needed in the preconception cohort than in an early pregnancy cohort and longer time is needed for a preconception cohort study. For example, the Shanghai Birth Cohort Study (www. shyousheng.net) recruited approximately 1200 preconception couples. By the end of a 12-month follow-up, approximatelyhalf of theparticipantswere infertile, had miscarried, were still not pregnant, or were lost to follow-up. Furthermore, couples who seek preconception care tend to be better educated and have higher socioeconomic status. Thus, the preconception sample is less representative of the general obstetric population than is the early pregnancy cohort. A hybrid design incorporating both preconception and early pregnancy cohorts may bemore practical and can serve different purposes. With its comprehensive MCH network, China can apply both hospital-based and community-based recruitment strategies. Hospital-based recruitment will be much more efficient when recruiting couples before or in early pregnancy. Conversely, to follow the children for a long time, the community-based approach has advantages. A combination of hospital-based recruitment and community-based child follow-up can make the best use of the system. Thus, the sampling strategies are likely to be complex. Great care must be taken when selecting participating hospitals to achieve a balance between efficiency and feasibility and population representativeness. Recruitment and biospecimen collection consume a substantial portion of the budget;