Sample

Gemini cohort data (a nationally representative twin study of early growth¹⁶) were used in this study. In total, 2402 of 6754 families (36% of those with live twin births in England and Wales during March-December 2007) gave written consent to participate and completed a baseline questionnaire when their children were a mean (SD) of 8.2 (2.2) months of age (range, 4–20 months). The HEI was completed by 1113 of 2402 families (46% of the total sample) when the children were a mean (SD) of 4.2 (0.4) years of age (range, 3–5 years). This study sample comprised 925 twin pairs (1850 twins) with data on all study variables. Data were analyzed from July to October 2013 and in June 2018. Ethical approval was granted by the University College London Committee for the Ethics of non–National Health Service Human Research. Data were deidentified.