Gemini is a large population-based study of twins designed to investigate the genetic and environmental influences on obesity risk, weight gain, and early growth. Gemini have followed twins and their families for over a decade, collecting detailed information about the twins’ growth, eating behaviours, appetite, and the home environment. A key aim of the Gemini study is to create a rich resource of data on early childhood exposures that can be used to assess the determinants of long-term health.

University College London

Geographic coverage - Nations
England, Wales

Geographic coverage - Regions

Start date

Catalogue record last updated


Sample type
Birth cohort (twin design)

Sample details
Families with twins born in England and Wales between March and December 2007 were approached on behalf of Gemini by the Office for National Statistics (N = 6,754) in January 2008. 3,435 families agreed to be contacted by the research team, with 2,402 families (36% of the target population) returning a completed baseline questionnaire. The sample comprises of 1,586 same-sex and 816 opposite-sex twin pairs.

Gemini families live across the whole of England and Wales, and the distribution mirrors the population density. The Gemini study includes twins that are comparable in sex, zygosity, gestational age, and birthweight to national averages of twins. However, mothers are somewhat older, and both parents are on average slightly healthier than the national population. As in many cohort studies, there is an over-representation of White–British families within the Gemini cohort.

Sample size at recruitment
2,402 families

Sample size at most recent sweep
987 twins, 492 parents (2020 - Time 9)


Age at recruitment
8 months

Cohort year of birth


Data access
Contact study team by emailing gemini@ucl.ac.uk to express an interest in accessing the data

Genetic data collected

Linkage to administrative data

Additional information


Related themes
Covid-19 data collection, Diet and nutrition, Education, Housing, Socioeconomic status and deprivation, Neighbourhood, Physical health assessment, Digital technology and social media, Puberty, Parenting and family, Sleep problems

Key Papers

Gemini: a UK twin birth cohort with a focus on early childhood weight trajectories, appetite and the family environment.

Medical Research Council
Cancer Research UK
Mental health measures timeline

Sweep name:

Cohort member age:

Data collection period:


Physical health measures:

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