Determination of the Iodine Status in Pregnant Women in the Netherlands. Are Current Iodine Intake Recommendations Still Adequate?

Rationale: Adequate dietary iodine intake is essential to thyroid hormone synthesis, which is key for normal growth, development and metabolism. During pregnancy, maternal iodine needs are increased (recommended intake: 175 µg/day) and iodine deficiency during pregnancy affects brain and cognitive development of the foetus and might lead to pregnancy complications. Despite the use of iodized salt, it has been shown that iodine intake in the Netherlands is declining. Importantly, a recent small study in Groningen indicated a high prevalence of iodine deficiency during pregnancy (83% of participants) which was not completely restored by 16-week iodine supplementation (150 ug/d). Also in other Western European countries (i.e. Belgium, U.K., North Ireland, Sweden, Denmark and Austria) low median urinary concentrations of iodine (73-124 ug/L) have been observed in pregnant women. Notably, most studies collected spot-urine samples and a 24h urine collection, the golden standard for determination of iodine status, is lacking. Therefore, here it is proposed to measure 24h median urinary iodine concentration corrected for urinary volume and creatinin levels in pregnant women, and compare these values with Thyroglobulin (Tg)-concentrations in serum as measure for iodine intake over a longer period of time. It is hypothesised that the iodine status of pregnant women in The Netherlands is lower than the national recommended intake for this target group.