title: [A longitudinal study regarding the gestational changes in iodine nutrition and thyroid function among pregnant women in the iodine deficient areas of Henan province].
abstract: OBJECTIVE
  To characterize the gestational changes of iodine nutrition and thyroid function and to explore the factors associated with the thyroid function in pregnant women.
  
  
  METHODS
  A longitudinal survey was conducted in 130 pregnant women in Luohe city of Henan province from October 2012 to May 2013. Samples of fasting blood and urine were collected in each trimester to test on thyroid function and urinary iodine. Data regarding social demography and lifestyle behavior were collected through questionnaire in the first trimester.
  
  
  RESULTS
  The medians of urinary iodine (MUI) for pregnant women were 238.9, 150.8 and 306.4 µg/L in the first, second and third trimesters, respectively (P < 0.05). With the increase of gestational age, the level of free triiodothyronine (FT3) showed no significant change (P > 0.05) but the level of free thyroxine (FT4) decreased (P < 0.05), with the level of thyroid stimulating hormone (TSH) increased and then declined (P < 0.05). A U-shaped curve were seen between iodine nutrition and thyroid function. With the increase of iodine level, the level of TSH first increased and then decreased while the levels of FT3 and FT4 showed the opposite trend. The level of TSH was influenced by factors as education level, history of chronic diseases, history of CT and X-ray examination, and intake of pickled food etc. The level of FT4 was associated with residence (urban or rural), stressful events in the previous year, daily means of transportation, and the hours of sedentariness, working and sleeping.
  
  
  CONCLUSIONS
  Significant differences were noticed in iodine nutrition and thyroid function of pregnant women during the three trimesters. It was essential to establish specific reference ranges for different trimesters. Thyroid functions of pregnant women seemed to be associated with iodine level and lifestyle.
authors: Henan Provincial Center for Disease Control and Prevention, Zhengzhou 450016, China. Email: yangjin6429@163.com.
authors: Jin
authors: J
authors: Yang
authors: Henan Provincial Center for Disease Control and Prevention, Zhengzhou 450016, China.
authors: Heming
authors: H
authors: Zheng
authors: Henan Provincial Center for Disease Control and Prevention, Zhengzhou 450016, China.
authors: Xiaofeng
authors: X
authors: Li
authors: Henan Provincial Center for Disease Control and Prevention, Zhengzhou 450016, China.
authors: Huili
authors: H
authors: Ying
mesh_terms: D005260:Female; D006801:Humans; D007454:Iodides; D007455:Iodine; D008137:Longitudinal Studies; D009752:Nutritional Status; D011247:Pregnancy / Q000502:physiology*; D011261:Pregnancy Trimester, First; D011263:Pregnancy Trimester, Third; D011264:Pregnancy Trimesters; D012016:Reference Values; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin; D013974:Thyroxine; D014284:Triiodothyronine
chemical_list: D007454:Iodides; D014284:Triiodothyronine; D013972:Thyrotropin; D007455:Iodine; D013974:Thyroxine