Introduction It is widely recognised that the UK birth cohorts have generated important new knowledge through life course analyses. However a new data resource is needed to advance understanding of the complex interplay between biology, behaviour, and environment during early development, and its influence on future health and well-being. An innovative design for a new UK Birth Cohort Study (BCS) was developed by a UK-wide investigator network in response to an open call for proposals. The preparatory phase will start in 2012.

Methods The new UK BCS will recruit over 90 000 pregnant mothers and their partners who will be seen during pregnancy and again, with their child, 4 months and 1 year after birth. Information, biological samples and biophysical assessments collected at these visits will be enhanced by linkage to obstetric records, environmental data collected from the home and a wide range of routine data sources. A further 20 000 pregnant women throughout the UK will be interviewed when their children are aged 4 months and again at 1 year to allow the larger sample to be related to the UK population as a whole. In contrast to earlier UK-wide birth cohorts, the UK BCS will: collect data and biological samples from children and their families before birth and in early childhood; capture the substantial demographic changes that have taken place in the UK in recent years; and have sufficient power to identify effects specific for different ethnic groups.