In 2010, 7.6 million children under the age of five died worldwide (Liu et al., 2012). Notably, the burden of under-five mortality varies dramatically by country. The majority of total child deaths in 2010 were seen in Africa (3.6 million) and southeast Asia (2.1 million deaths), compared to 0.16 million and 0.28 million under-five deaths in Europe and the Americas, respectively (Liu et al., 2012). Strikingly, nearly half of the world's under-five child deaths in 2010 could be attributed to only five countries: India, Nigeria, Democratic Republic of the Congo, Pakistan, and China (Liu et al., 2012). In Pakistan alone, over 420,000 under-five child deaths occurred in 2010 (Liu et al., 2012).
A thorough understanding of the etiology of child mortality is necessary to guide research efforts aimed at tackling this important global health problem. Importantly, in 2010, the causes of only 2.7% (0.205 million) of all deaths in children under the age of five were medically certified (Liu et al., 2012), highlighting the need to gather high-quality data on the causes of mortality.
Prospective longitudinal birth cohort studies present an opportunity to examine temporal relationships between early-life exposures (i.e. prenatal, pregnancy, and early postnatal exposures) and multiple health and non-health related outcomes including mortality, morbidity, and socioeconomic position. It is well documented that exposures that occur early in life, including genetic, environmental, socioeconomic, and lifestyle factors, may have long-lasting effects on growth, development, and health outcomes throughout an individual's entire life course (Lynch \& Smith, 2005). Thus, data on exposures during pregnancy and early childhood are valuable and may provide clues to the etiology of long-term outcomes.
Additional value can be gained through cross-cohort collaborations and comparisons (Larsen et al., 2013)(Paternoster et al., 2012)(Brion et al., 2011). By pooling data from multiple cohort studies, causal inferences can be made with greater confidence. In addition, through cross-country comparisons, heterogeneity in exposures is often increased making it more likely that an association between exposure and outcome will be observed. Similarly, cross-cohort comparisons enable researchers to investigate patterns associated with health, social, and economic outcomes in distinct regions of the world. These types of analyses may provide valuable insight into the underlying causes of global health inequalities.
The objective of this study is to implement a longitudinal prospective birth cohort study in Pakistan to obtain extensive and high-quality information on early-life exposures and health and non-health related outcomes in the first year of life. Concurrent to the design and implementation of this cohort study in Pakistan, similar studies are being implemented in Kenya (Coastal Region Cohort, Lead PI: Dr. Shaun Morris), Brazil (Pelotas Cohort, Lead PIs: Dr. Pedro R.C. Hallal, Dr. Diego G. Bassani and Dr. Mariangela Silveira), and South Africa (Birth to Twenty Cohort, Lead PI: Dr. Shane Norris). The investigators of each project have communicated their intent to align study materials in an effort to increase the ease of future comparisons between findings. This study will therefore be one crucial pillar in a multi-country cross-cohort comparison and presents a unique opportunity to investigate and compare the patterns that shape health and non-health related outcomes in individuals from four distinct regions in the world.
