Iodine status, thyroid function and pregnancy: study of Swedish and Sudanese women

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 AE 5.4 y and 66.3 AE 12.9 kg respectively. The corresponding ®gures for the Sudanese women were 28.0 AE 4.9 y and 64.8 AE 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. No signi®cant 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 signi®cantly lower mean TSH values than the Swedish women in weeks 36±39 of pregnancy (P`0.02), and signi®cantly 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.

Changes in iodine metabolism during late pregnancy and lactation: a longitudinal study among Sudanese women

“…The current study is complementary to the comprehensive studies on iodine nutrition among pregnant women that we have conducted previously in Sudan and Sweden (Elnagar et al, 1998;Eltom et al, 1999a,b). In these studies we looked at the changes in the thyroid function associated with pregnancy in populations residing in areas with variable amounts of iodine intake as represented by these two countries.…”

“…In a previous investigation of Swedish and Sudanese pregnant women, we found that the Swedish women showed a decline in FT4 and a rise in TSH with the progression of pregnancy, while the Sudanese women with (Eltom 1999a,b) and without (Elnagar et al, 1998) goitre displayed a reduction both in FT4 and in the urinary iodine concentration (UIC), but a stable TSH within the reference range. Our interpretation of those ®ndings, as in similar other studies, was that both of these groups of pregnant women, although exhibiting different behaviour in their iodine metabolism in response to pregnancy, were likely to be in need of additional iodine intake during gestation.…”

Seasonality in urinary and household salt iodine content among pregnant and lactating women of the plains of Nepal

“…Within each season, differences in UI between pregnant and lactating women were significant by median two-sample test, Po0.005. (Pedersen et al, 1993;Glinoer et al, 1995;Caron et al, 1997;Elnager et al, 1998) and Sudan (Elnager et al, 1998;Eltom et al, 2000). However, compared to European women, women in this region of Nepal are subject to additional environmental and nutritional stresses (West et al, 1999;Dreyfuss et al, 2000) that may compound the health consequences of mild-to-moderate iodine deficiency for themselves and their offspring.…”

Trimester-specific reference intervals for thyroxine and triiodothyronine in pregnancy in iodine-sufficient women using isotope dilution tandem mass spectrometry and immunoassays

“…All the women were on normal diets and did not suffer from severe hyperemesis nor any known thyroid disease. Sweden is an iodine-sufficient country, and although urinary iodine (UI) concentrations were not specifically measured in the women participating in our study, in another study conducted in Sweden in 1998 [19], mean values (95% confidence interval) for 24-h urine during gestation week (GW) 11-13 were 1.40 (1.19-1.61) μmol/day, GW 24 UI 1.33 (1.14-1.51) μmol/day, GW 32, UI 1.45 (1.06-1.84) μmol/day and GW 38 UI 1.14 (0.88-1.39) μmol/day. Serum samples were stored frozen at −70 °C and thawed at room temperature, and all samples were analyzed at the same time.…”