Swedish Iodine in Pregnancy and Development in Children (SWIDDICH) Study

  • End date
    Jun 30, 2032
  • participants needed
  • sponsor
    Göteborg University
Updated on 30 September 2021


THE ULTIMATE GOAL of this project is to answer the question "In MILD IODINE DEFICIENCY (ID), should 150 g iodine/day be administered to pregnant women with a normal diet, to attain a normal cognitive development of the fetus or is there no cognitive deficit from mild ID and no extra iodine is needed?". To answer this question, the investigators planned a randomized, placebo-controlled trial of iodine supplementation during pregnancy in Sweden (SWIDDICH) with the follow-up of childrens' COGNITIVE DEVELOPMENT at 18 months, 3.5, 7 and 14 years.

Iodine deficiency (ID) is associated with thyroid morbidity and, especially in children, with impaired cognitive development. Sweden introduced iodine fortification of table salt 1936 and mental retardation due to severe ID is eradicated. Is mild ID during pregnancy also eradicated? If not, is this of importance? A national study performed by the investigators in 2007 showed iodine sufficiency in general population, but there are no pregnancy data. Local studies have raised concerns for mild ID during pregnancy in Sweden and a trans-sectional national study is currently ongoing.

The burning question for Sweden and the whole world is: is mild ID during pregnancy of importance for the developing brain of the fetus? Two large observational studies have shown association between mild ID during pregnancy and lower verbal IQ or educational performance at school-aged children. The world needs a randomized placebo-controlled trial (RTC) comparing the cognitive outcome in children exposed to mild ID during fetal life with children exposed to normal iodine levels during fetal life.

Our HYPOTHESIS is that pregnant women in Sweden have mild ID and that children exposed to mild ID during fetal life have a lower cognitive development, compared to children to mothers taking 150 ug iodine supplementation during pregnancy.

The MAIN AIM of the SWIDDICH trial is to determine if children exposed to mild iodine deficiency (ID) during fetal life achieve worse cognitive development compared to children exposed to normal iodine status reached by maternal iodine supplementation.



  • To determine if children exposed to mild iodine deficiency (ID) during fetal life achieve worse cognitive development compared to children exposed to normal iodine status reached by maternal iodine supplementation.
  • To compare urinary iodine concentration (UIC), thyroglobulin (Tg), free tetraiodothyronine (FT4) and thyroid stimulating hormone (TSH) in pregnant women on 150 g iodine or placebo
  • To compare milk iodine concentration (MIC) in colostrum, and TSH in the first 200 newborn children to pregnant women receiving 150 g iodine or placebo


Iodine deficiency increases the risk for hypothyroidism and goiter and during the pregnancy for abortion or cognitive and other abnormalities of the baby. According to the WHO recommendations, UIC during pregnancy should be 150-249 ug/L. In 2007 a national study showed iodine sufficiency in Swedish general population. It is debated whether or not iodine shall be given to pregnant women in iodine sufficient populations.

The research group started this randomized iodine intervention in pregnant women in 2012. The first hypothesis was that iodine supplementation of 150 g/day is needed during pregnancy in Sweden in order to ensure normal iodine and thyroid hormone status in mothers and newborn children and that pregnant women in Sweden suffer from mild iodine deficiency (ID).

There is a substantial gap of knowledge with regards to whether mild ID during fetal life entails negative consequences on cognition. Two large observational studies have shown association between mild ID during pregnancy and lower IQ or educational performance in school-children. The only two randomized placebo-controlled trials (RCTs) studying mild ID in pregnancy were either too small for safe conclusions to be drawn ( Brucker-Davis et al, n=86), or did not manage to separate groups based on iodine levels (the MITCH study, Melse-Boonstra et al, n=839). The need for a RCT with sufficient sample size remains. This led the research team to form a second hypothesis within the trial: children exposed to mild ID during fetal life have lower cognitive development compared to children to mothers taking 150 ug iodine supplementation during pregnancy. The decision to expand the trial was made and the target number of participants to be recruited increased from 200 to 1275 in order to reach enough power to follow-up the childrens' cognitive development.



This is a prospective placebo-controlled trial of children whose mothers got iodine supplement 150 g/day or placebo (a multivitamin preparation without iodine) during pregnancy (week 102 until delivery). The target number participants during pregnancy is 1275 to enable sufficient power in the children follow-up (n=788). The main outcome is intelligence quotient (IQ) at 7 year of age. Cognitive development in children will be also assessed at 18 months, 3.5, and 14 years.

Pregnancy part

Pregnant women from more than ten maternity care centers in Sweden are randomized to daily receive a multivitamin tablet with 150 g iodine or placebo (multivitamin without iodine). The intervention starts at pregnancy week 8-12 and ends directly post-partum for the first 200 women and at pregnancy week 362weeks for the remaining participants. This time point may be adjusted to local circumstances, depending on when during the third trimester the routine visit at maternity care center takes place. Participants are included after the first visit by a midwife. Urine sample for UIC and U-creatinine, and blood sample for thyroid hormones, thyroid stimulating hormone (TSH), thyroglobuline (Tg) and thyroperoxidase antibodies (TPO-ab) are collected and a simple questionnaire is filled in at week 102 weeks of pregnancy and placebo/iodine is started. Selenium and iron is also measured. The same measurements are collected in week 251 week and week 362 weeks. Directly after delivery (within 5 days), MIC and UIC in the first 200 mother as well as UIC and TSH in their newborn child were collected and a simple questionnaire is filled in. Weight, length and APGAR in the child and pregnancy complications are registered. Blood is also frozen for future analyses and access to medical files is accepted.

In parallel 90 healthy female controls from Skaraborg area stratified for age and smoking habits are collected from a randomized sample attained by the Swedish Tax Agency. UIC, u-creatinine, FT4, TSH, Tg, TPO-ab, and samples to be frozen are collected and a questionnaire is filled in. Selenium and iron is analyzed in blood sample from the first 200 pregnant women and from controls. The primary purpose for having a control population is to ascertain that the normal population in the area of Skaraborg is iodine sufficient.

Children follow-up

At 18 months 1 month psychomotor development is assessed by means of ASQ (Ages and Stages Questionnaire). At 3,5 years 2 months the IQ is measured (WPPSI-IV), behavior is assessed (CBCL questionnaire) and urine is collected for UIC measurement. At 7 years 3 months the following are assessed: IQ (WISC IV), motor development (Movement ABC), behavior (CBCL), symptoms related to attention deficit and hyperactivity disorder (ADHD, 5-15 Nordic questionnaire). Additionally, at 7 years 3 months urine is collected for UIC measurement, blood sample is taken for thyreoglobulin (Tg), thyroid hormones and deiodinases, and MRI of the brain is performed in a subsample. At 14 years 6 months all these, except for the Movement ABC, are repeated. On all occasions information on socio-economic status and other possible confounders are collected by means of questionnaires filled by parents and by children (14 years).

Condition Pregnancy, Cognitive Developmental Delay, Thyroid Gland; Node
Treatment Placebo, iodine
Clinical Study IdentifierNCT02378246
SponsorGöteborg University
Last Modified on30 September 2021


Yes No Not Sure

Inclusion Criteria

Age 18-40 years
Agreeing not to take iodide containing supplements 1 week prior to the collecting of the samples

Exclusion Criteria

Current thyroid disease
Risk factors for thyroid disease (history or heredity for thyroid or other autoimmune disease or symptoms of hypo-/hyperthyroidism) where the TSH is abnormal
Possibility to not attend to the protocol according to the investigator's opinion
Currently pregnant or lactating
Less than 6 months from previous pregnancy or lactating period
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