Table 2.

Summary of SWIDDICH study actions

Time point	Pregnancy				Child follow-up
	First pregnancy visit (<12 weeks)	Weeks 7–12	Weeks 25–28	Weeks 34–38	18 months	3.5 years	7 years	14 years
Enrolment
Information given	X
Eligibility screen	X
Informed consent	X
Allocation		X
Intervention
Iodine 150  µg or placebo in multivitamins
Assessments	First pregnancy visit (<12 weeks)	Weeks 7–12	Weeks 25–28	Weeks 34–38	18 months	3.5 years	7 years	14 years
Urinary iodine concentration		X	X	X		X	X	X
Thyroid function*		X	X	X			X	X
Milk iodine concentration
Cognition  IQ						X WPPSI	X WISC	X WISC
Behaviour						X CBCL	X CBCL Nordic 5–15	X CBCL Nordic 5–15
Psychomotor development					X ASQ-3		X Mov ABC
Brain MRI (subgroup)							X	X
Background information
EUthyroid SES questionnaire adults					X	X	X	X
EUthyroid SES questionnaire children								X
Own questionnaire		X	X	X	X	X	X	X

*FT4 TSH, thyroglobulin: serum sampling during pregnancy and dry blood spot sampling during children follow-up.

ASQ, The Ages and Stages Questionnaire; CBCL, Child Behavior Checklist; EUthyroid SES questionnaire, Socioeconomic Status questionnaire, validated by EUthyroid foundation; Mov ABC, Movement Assessment Battery for Children; SWIDDICH, Swedish Iodine in Pregnancy and Development in Children; WISC, Wechsler Intelligence Scale for Children; WPPSI, Wechsler Preschool and Primary Scale of Intelligence.