Thyroid function and iodine nutrition in women during pregnancy and in their neonates : Studies among Sudanese subjects

Sammanfattning: The studies described in this thesis were carried out in Sudan and Sweden. Pregnant Sudanese women, who had a significantly lower urinary iodine concentration than their Swedish counterparts, showed significantly lower thyrotrophin (TSH) levels in weeks 36-39 of pregnancy and higher free thyroxine (FT4) levels both in weeks 20-24 and 36-39 of pregnancy than Swedish pregnant women. This indicates that determination of urinary iodine alone may not give adequate information about thyroid hormone status. The pattern of thyroid function among the Sudanese women suggests the existence of an adaptive mechanism to provide a better utilisation of iodine in a situation of mild iodine deficiency.Sudanese pregnant women with goitre showed evidence of hypothyroxinaemia in late pregnancy, with reduced FT4 and urinary iodine concentration levels compared to the control group. TSH did not differentiate the goitrous pregnant women from the non-goitrous healthy controls.The Sudanese and Swedish pregnant women had significantly higher median thyroglobulin (Tg) levels in the third trimester than the control groups. The Sudanese pregnant women had significantly higher median Tg levels than the Swedish pregnant women in all the three trimesters of pregnancy. TSH failed to differentiate between the different urinary iodine concentration groups. Tg is a useful indicator of iodine status during pregnancy.Neonatal thyroid function parameters, except triiodothyronine (T3), were significantly higher than the corresponding maternal ones during labour. This suggests that the thyroid gland of the newborn has to be stimulated to achieve optimal FT4 levels. The thyroid function of neonates born of mothers with elevated Tg was similar to that of neonates of mothers with low Tg levels. This may partly explain the autonomy of the foetal thyroid-pituitary axis.Maximum maternal thyroidal stimulation was observed in the Sudanese mothers 3 months postpartum, possibly as a result of persistence of pregnancy-induced changes and the sequestration of some of the maternal iodine pool to the breast milk. The thyroid function was restored to the pre-pregnancy state nine months post-partum.