Population-based Study On Iodine Status And Thyroid Function In Pregnant Women From Areas With Different Iodine Levels

Objective Pregnant women generally are the susceptible population.This study intends to clarify the changes of iodine nutritional status and thyroid function in pregnant women with different iodine nutrition,and to explore the relationship between iodine nutrition and thyroid function in pregnant women in different trimester,in order to provide data for guiding pregnant women to maintain proper iodine nutritional status.Subjects and Method A cross-sectional epidemiological investigations in this study were conducted on healthy pregnant women aged 20-35 years old in Tianjin and Shandong.Pregnant women were recruited according to the inclusion and exclusion criteria.The basic information and dietary questionnaire survey were collected,and a disposable random urine sample was collected to evaluate the iodine nutritional status.The thyroid gland volume was measured and defined goiter.A-5mL morning fasting blood sample was collected to measure thyroid function parameters.Follow up was performed on the offspring of eligible pregnant women.Results In this study,1997 healthy pregnant women were recruited from Tianjin and707 healthy pregnant women from Gaoqing.According to the inclusion and exclusion criteria,2470 healthy pregnant women were included in the analysis.The iodine concentration of drinking water was less than 15?g/L in Tianjin.465 drinking water samples from Shandong were collected to measure the iodine content,and the median of water iodine content was 199.5?69.9,362.3??g/L,which was high water iodine area and without iodized salt supplied.1742 disposable spot urine samples were collected.The median urinary iodine concentration?UIC?of pregnant women was 158?107,229??g/L.513 urine samples of pregnant women were collected in Shandong Province.The median UIC was 244?141,425??g/L.The UIC of pregnant women in Shandong was significantly higher than that in Tianjin?p<0.0001?.According to World Health Organization criteria for determining iodine nutrition in pregnant women,the iodine nutrition of pregnant was adequate.During pregnancy,the UIC of pregnant women in Tianjin decreased significantly with the progression of pregnancy?p<0.0001?,while the UIC of pregnant women in Shandong was not significantly changed?p=0.21?.1807 blood samples of pregnant women were collected to measure thyroid function parameters.The levels of free triiodothyronine?FT₃?of pregnant women living in Tianjin were4.3±0.6pmol/L,free thyroxine?FT₄?were 14.8±2.1pmol/L,thyrotropin?TSH?were1.5?1.0-2.2?mIU/L and thyroglobulin?Tg?were 10.4?5.9-17.2??g/L,respectively.The positive rate of thyroid peroxidase antibody?TPOAb?were 4.1%and thyroglobulin antibodies?TGAb?were 4.2%,respectively.The levels of FT₃,FT₄,TSH and Tg in pregnant women from Gaoqing were 4.1±0.7 pmol/L,14.5±2.5pmol/L,1.8?1.1,2.5?mIU/L and 10.5?6.3,16.9??g/L,respectively.The positive rate of TPOAb and TGAb was 6.3%and 3.3%,respectively.The serum level of FT₃ and FT₄ in pregnant women in Tianjin and Shandong increased along with the progress of pregnancy?p<0.0001?.The serum TSH level in pregnant women in Tianjin decreased along with the progress of pregnancy?p<0.0001?but the serum TSH level in pregnant women in Shandong was increased along with the progress of pregnancy?p=0.003?.In addition,the serum TSH level of pregnant women in the first and second trimester in Shandong were higher than those in Tianjin?p=0.0003;p<0.0001?,however,no statistical difference found in the third trimester between two regions.In this study,34 pregnant women?1.5%?were diagnosed with subclinical hypothyroidism.There was a significant difference between Tg and thyroid volume?Tvol?in pregnant women under different UICs?p<0.0001?.A significant difference was found in the prevalence of goiter in pregnant women with different UICs?p<0.0001?,and the prevalence of goiter significantly increased with the increase of UIC.When the UIC?500?g/L,the prevalence of goiter reached 14.6%.When stratified by trimester,in the first trimester,no significant difference in thyroid hormone related indicators under different UICs?p>0.05?but there was a significant difference in thyroid volume?p=0.006?.In the second trimester,no significant differences were found?p>0.05?.In the third trimester,serum Tg decreased significantly along with UIC?p=0.044?,and thyroid volume was also significant different?p<0.0001?.There was a significant difference in the incidence of goiter in the first trimester with different UICs?p=0.0033?.No difference was observed in the second trimester?p=0.08?.There was a significant difference in the incidence of goiter in the third trimester with different UICs?p<0.0001?and the lowest prevalence rate?2.2%?was found in UIC of100-149?g/L.There was no statistical difference in the incidence of subclinical hypothyroidism and Tg>40?g/L in different UICs?p>0.05?.In the follow-up study of participate pregnant women in Tianjin,1453?76.7%?pieces of delivery information were collected.It was found that no significant difference in height,the weight and the heel blood TSH level of neonates in pregnant women with different iodine nutrition.Conclusions 1.The UIC of pregnant women living in high iodine water area was higher,and high in each trimester.2.The UIC of pregnant women with sufficient iodine nutrition remained relatively stable throughout pregnancy,while the UIC of pregnant women with slightly iodine deficiency decreased during pregnancy,which indicated that iodine deficiency may severe in third trimester.3.The thyroid function parameters varied during pregnancy.High iodine intake leaded to serum TSH increase during pregnancy,especially during the first and second trimester.4.Pregnant women in late pregnancy were more likely to get thyroid dysfunction due to long exposure to iodine nutrition.