Preconception Maternal Iodine Status and Offspring Cognitive Function:

Adverse effects of severe maternal iodine deficiency in pregnancy on fetal brain development are well-established, but the effects of mild or moderate deficiency are not well understood. To date, most studies have examined iodine status in pregnancy; less is known about maternal iodine nutrition before conception, and this study aims to address that gap in information

The Southampton Women's Survey (SWS) is a prospective study of mothers and children, established in 1998. A general population sample of 12,583 non-pregnant women, aged 20-34 years resident in Southampton was recruited (1998-2002). All women were visited at home by a research nurse and characterised in detail, including assessments of diet, lifestyle and body composition. Between 1998 and 2007, 3158 of the SWS women became pregnant, and went on to deliver a live singleton infant. These women were followed up in through pregnancy and their children have been assessed in a number of follow-up studies in infancy and childhood. These have included repeated assessments of diet, anthropometry and body composition, as well as detailed functional measurements at specific ages, and are ongoing.

At the 6-7 year assessment, the children's cognitive function was measured and this is the primary outcome.

Spot urine samples were collected from the SWS women at clinic visits following their initial interviews (median 33 (IQR 15-87) days), in the period before conception. The time of day was recorded for each urine collection. Urine samples were split divided into aliquots on the day of collection. They were frozen and stored at -80⁰oC from the date of collection until being thawed and assayed for iodine and creatinine contents in 2016 by the Trace Element Unit, Southampton General NHS Trust Hospital, Southampton, UK.

Inclusion criteria

• Offspring of women recruited to the Southampton Women's Survey
• Aged 6-7 years at time of measurement

Exclusion criteria

• Mother had not provided urine sample before conception of the child