Iodine status during pregnancy and at 6 weeks, 6, 12 and 18 months post-partum

Abstract

Iodine deficiency during pregnancy and in the post-partum period may lead to impaired child development. Our aim is to describe iodine status longitudinally in women from pregnancy until 18 months post-partum. Furthermore, we explore whether iodine status is associated with dietary intake, iodine-containing supplement use and breastfeeding status from pregnancy until 18 months post-partum. We also assess the correlation between maternal iodine status 18 months post-partum and child iodine status at 18 months of age. Iodine status was measured by urinary iodine concentration (UIC) during pregnancy (n = 1,004), 6 weeks post-partum (n = 915), 6 months post-partum (n = 849), 12 months post-partum (n = 733) and 18 months post-partum (n = 714). The toddlers' UIC was assessed at 18 months of age (n = 416). Demographic variables and dietary data (food frequency questionnaire) were collected during pregnancy, and dietary data and breastfeeding practices were collected at all time points post-partum. We found that iodine status was insufficient in both pregnant and post-partum women. The UIC was at its lowermost 6 weeks post-partum and gradually improved with increasing time post-partum. Intake of milk and use of iodine-containing supplements significantly increased the odds of having a UIC above 100 μg/L. Neither the mothers' UIC, vegetarian practice, nor exclusion of milk and dairy products were associated with the toddlers UIC 18 months post-partum. Women who exclude milk and dairy products from their diets and/or do not use iodine-containing supplements may be at risk of iodine deficiency. The women possibly also have an increased risk of thyroid dysfunction and for conceiving children with nonoptimal developmental status.

Keywords: breast feeding; iodine intake; post-partum period; pregnancy; toddlers; urinary iodine concentration.

FIGURE 1

Urinary iodine concentration (UIC) at the different data collection waves. Cases with UIC > 500 μg/L were excluded from the figure. The blue lines indicate the cut‐off used by the WHO to assess adequate iodine status from UIC in pregnant (150 μg/L) and lactating women (100 μg/L). Boxes indicate the upper (p75) and lower (p25) quartile, with the thick black line giving the median (p50). The T‐bars indicate 1.5 × length of the box (interquartile range). The filled circles are outliers defined as a value > 1.5 length of the box. The asterisks are extreme outliers defined as a value > 3.0 length of the box