Abstract
Objective: To examine and compare the effects of pregnancy on the thyroid hormone homeostasis in two different populations with variable iodine supply.
Design: A longitudinal prospective cohort study throughout pregnancy involving Swedish and Sudanese pregnant women.
Setting: The subjects were enrolled consecutively during their antenatal follow-up at health centres at Nyby in Uppsala, Sweden and Omdurman in Sudan.
Subjects: Fifty-one apparently healthy women from Uppsala, Sweden and twenty-eight pregnant women from Omdurman, Sudan were recruited during pregnancy. The mean age and weight of the Swedish women at the beginning of pregnancy were 29.9±5.4 y and 66.3±12.9 kg respectively. The corresponding figures for the Sudanese women were 28.0±4.9 y and 64.8±9.4 kg respectively.
Methods: Blood samples were drawn on four occasions from the Swedish group at 11–13, 24, 32, and 38 weeks of pregnancy, and on three occasions from the Sudanese group at 10–12, 20–24, and 36–39 weeks. Twenty-four hour urine samples were collected from the same subjects and on the same occasions as blood sampling. The urine samples were kept in a refrigerator until the volumes were measured, after which 20 mL aliquots were taken and kept frozen until analysed.
Main outcome measures: Twenty-four hour urinary iodine output, TSH, FT4 and T3.
Results: The 24 h urinary iodine output at the different times during gestation were higher among the Swedish women, with mean values (95% confidence interval) of 1.40 (1.19–1.61), 1.33 (1.14–1.51), 1.45 (1.06–1.84) and 1.14 (0.88–1.39) μmol/d, than among the Sudanese cohort, with corresponding values of 0.49 (0.27–0.72), 0.29 (0.19–0.39), 0.56 (0.25–0.88) μmol/d. No significant changes in daily urinary iodine loss were observed in the two groups with progression of pregnancy. However, in the Swedish women the mean free T4 concentration fell from 11.81 pmol/l at the beginning of pregnancy to 8.82 pmol/l and the mean TSH rose from 1.11–1.95 mU/l between the beginning and end of pregnancy. Such changes were not detected among the Sudanese women, who had significantly lower mean TSH values than the Swedish women in weeks 36–39 of pregnancy (P<0.02), and significantly higher FT4 values than the Swedish women both in weeks 20–24 and in weeks 36–39 (P<0.005 and P<0.001) respectively.
Conclusions: The study suggests that determination of urinary iodine alone gives inadequate information about the capacity of an individual to utilize an available iodine supply and it also shows the existence of different patterns of thyroid response during pregnancy. The history of iodine availability prior to and during pregnancy seems to be an important determinant of the mechanism of thyroid gland response to ensure the extra iodine needed by the growing fetus.
Sponsorship: Financial support for this work was provided by the Swedish Medical Research Council and InDevelop AB, Uppsala University.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Elnagar, B., Eltom, A., Wide, L. et al. Iodine status, thyroid function and pregnancy: study of Swedish and Sudanese women. Eur J Clin Nutr 52, 351–355 (1998). https://doi.org/10.1038/sj.ejcn.1600563
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/sj.ejcn.1600563
Keywords
This article is cited by
-
A randomized, double-blind study of iodine supplementation during pregnancy in Sweden: pilot evaluation of maternal iodine status and thyroid function
European Journal of Nutrition (2021)
-
Iodine deficiency in pregnant women in Sweden: a national cross-sectional study
European Journal of Nutrition (2020)
-
Maternal Urinary Iodine Concentration and Pregnancy Outcomes: Tehran Thyroid and Pregnancy Study
Biological Trace Element Research (2020)
-
A Paleolithic-type diet results in iodine deficiency: a 2-year randomized trial in postmenopausal obese women
European Journal of Clinical Nutrition (2018)
-
Iodine nutritional status of women in their first trimester of pregnancy in Catalonia
BMC Pregnancy and Childbirth (2017)