The 2-BIG is a twin birth cohort study located in Guangzhou, China.Its initial aim is to facilitate research on understanding the interplay between genes and environmental factors on disease etiology. Data are collected regarding environmental, family and lifestyle exposures on twins from birth to 18 years old. Biological samples including blood and tissue samples are also collected from the twins and their parents.

Twins share the same intrauterine environment and the early family environment. When conducting research of chronic disease etiology, twins cohort can be a good control of bias from age, gender, genetic and early environment. Twin-based designs provide an estimate of the relative contribution of genetic and non-genetic factors to a specific phenotype. Twins study has an advantage of calculating heritability of traits. Since heritability of traits is various from different populations. It is important to establish database to calculate the heritability of traits associated with chronic major diseases in Chinese population. Twins cohort is rare in China at present. Therefore, extensive information including physical characteristics, mental health, and behaviors is collected from both twins and their parents. Longitudinal follow-up and surveillance of common diseases are also to be conducted. The 2-BIG aims to explore epigenetic markers and genes related to health status, as well as gene-environment interactions on diseases, both in intrauterine and childhood stages, especially in Chinese population.

Inclusion Criteria:

1. Live twins delivered in Guangzhou Women and Children's Medical Center
2. Permanent residents or families intended to remain in Guangzhou with their children for no less than 3 years
3. Baseline information during pregnancy available

Twins delivered in Guangzhou, China and their parents