Iodine status of pregnant women living in urban Johannesburg, South Africa

Abstract

Adequate intake of iodine is important during pregnancy because of its essential role in foetal growth and neurodevelopment. Data on iodine status of South African pregnant women are scarce, and the salt reduction policy implemented in 2016 may decrease iodine intake of South Africans. This cross‐sectional study assessed the iodine status of pregnant women residing in urban Johannesburg, South Africa. A total of 250 pregnant women were enrolled into the ‘Nutrition during Pregnancy and Early Development’ (NuPED) study and 312 pregnant women into the ‘Assessment of dried blood spot thyroglobulin in pregnant women to redefine the range of median urinary iodine concentration that indicates adequate iodine intake, South Africa’ (STRIPE‐SA) study and were included in this analysis. Urinary iodine concentration (UIC) was analysed in a spot urine sample. Thyroglobulin (Tg) was measured in serum, and thyroid‐stimulating hormone (TSH) and total thyroxine (tT4) were measured in dried blood spots. The median [interquartile range (IQR)] UIC of pregnant women was 144 (84–234) μg/L. Women in the first (n = 99), second (n = 262) and third (n = 174) trimester had a median UIC of 133 (81–316), 145 (84–236) and 156 (89–245) μg/L, respectively (p = 0.419). Median TSH, tT4 and Tg were 2.7 (2.3–3.2) mU/L, 202 (163–236) nmol/L and 9.2 (5.4–17.9) μg/L, respectively. Based on the median UIC, pregnant women residing in urban Johannesburg may be borderline iodine deficient. These findings highlight the need for ongoing monitoring of iodine status among vulnerable pregnant women, especially considering the recently introduced salt reduction policy in South Africa.

A Scoping Review of Iodine and Fluoride in Pregnancy in Relation to Maternal Thyroid Function and Offspring Neurodevelopment

“…A similar decrease in UIC and T3 throughout pregnancy was observed in a study of 215 pregnant women in China, although TSH was found to have a U-shaped curve with gestational age [ 73 ]. This is in contrast to a study of South African women ( n = 562) that found UIC increase in each trimester (133 μg/L, 145 μg/L, and 156 μg/L) [ 74 ]. Another study completed in Turkey measured newborn UIC and found 51% of newborns were I deficient [ 75 ].…”

“… Siro et al. [ 74 ] Observational South Africa Iodized salt fortification program is in use, but salt reduction legislation has decreased intake N/A Increased UIC throughout pregnancy. Vural et al.…”

An update: maternal iodine supplementation, thyroid function tests, and child neurodevelopmental outcomes

“…In a 2022 observational study in Turkey in a marginally iodine sufficient population, UIC decreased throughout pregnancy with a concomitant increase in TSH, which remained within normal limits, but was associated with a decrease in T3 and T4 [49]. A 2021 observational study in an iodine-sufficient population in rural China found a similar decrease in UIC and T3 throughout pregnancy, but a U-shaped curve with TSH [50], while a 2020 observational study in South Africa with a salt iodization program in place found an increase in UIC throughout pregnancy [51].…”