Table 1 Baseline characteristics

Recruitment state or territory

Australian Capital Territory/ New South Wales/ Queensland/ South Australia/ Tasmania/ Victoria/ Western Australia

Age, years

–

Gestation at enrolment, weeks

–

Parity

0/1/> 1

Multiple pregnancy

Yes/no

Pre-pregnancy BMI, kg/m²

–

Born in Australia

Yes/no

Aboriginal or Torres Strait Islander

Yes/no

Completed secondary education

Yes/no

Completed further study

Yes/no

Highest qualification completed

Certificate, apprenticeship or diploma/degree/higher degree/not applicable

Annual household income ($AUD)

 ≤ $25,000/$25,001 to $50,000/$50,001 to $100,000/$100,001 to $150,000/$150,001 to $250,000/> $250,001/undisclosed

Index of Relative Socioeconomic Disadvantage^a

Quintile 1/2/3/4/5

Smoking at enrolment

Yes/no

Smoking in 3 months leading up to pregnancy

Yes/no

Smoking in household at enrolment

Yes/no

Alcohol use at enrolment

Yes/no

Alcohol use in 3 months leading up to pregnancy

Yes/no

Fertility treatment

Yes/no

Type 1 diabetes

Yes/no

Type 2 diabetes

Yes/no

Gestational diabetes in previous pregnancy

Yes/no/not applicable

Pre-eclampsia/eclampsia in previous pregnancy

Yes/no/not applicable

Urinary iodine concentration, µg/L

–

Iodine intake at screening, µg/day^b

–

Pre-conception supplement use

Yes/no

Supplement use at enrolment

Yes/no

Infant sex

Female/male