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

AIMS

• To determine if children exposed to deficient micronutrition including 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 investigate the interaction between iodine, selenium and iron, as components of the intervention.
• To compare urinary iodine concentration (UIC), thyroglobulin (Tg), free tetraiodothyronine (FT4) and thyroid stimulating hormone (TSH) in pregnant women on daily tablet with vitamins and minerals, including 150 µg iodine or placebo
• To compare milk iodine concentration (MIC) in colostrum, and TSH in the first 200 newborn children to pregnant women receiving daily tablet with vitamins and minerals, including 150 µg iodine or placebo

BACKGROUND 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 daily supplementation with a tablet with vitamins and minerals including 150 µg iodine 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 deficient micronutrition including mild ID during fetal life have lower cognitive development compared to children to mothers taking a daily tablet with vitamins and minerals including150 ug iodine 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.

METHODS

Design

This is a prospective placebo-controlled trial of children whose mothers got iodine supplement 150 µg/day (a tablet with vitamins and minerals) or placebo (a multivitamin preparation without minerals) during pregnancy (week 10±2 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 3.5 year of age. Cognitive development in children will be also assessed at 18 months, 7, 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 minerals, including 150 µg 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 36±2weeks 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 10±2 weeks of pregnancy and placebo/intervention is started. Selenium and iron are also measured. The same measurements are collected in week 25±1 week and week 36±2 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 will be 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).