The SWS is a birth cohort study investigating the influence of maternal dietary, lifestyle, intrauterine, genetic, and epigenetic factors on children’s health and development, as well as on the health of the mothers themselves. Between 1998 and 2002, the study recruited over 12,500 non-pregnant women aged 20 to 34 years from Southampton, England. Babies born to the recruited women before June 2005 were also recruited into the study. The women and their babies were followed up twice during pregnancy and nine times following birth. A subgroup of the cohort was also followed up during the COVID-19 pandemic.