title: Urinary iodine in early pregnancy is associated with subclinical hypothyroidism in Tianjin, China: an observational study.
abstract: BACKGROUND
  Subclinical hypothyroidism (SH) is associated with adverse obstetric outcomes and neurodevelopment disorders. Both iodine deficiency and excess are associated with SH; however, few data regarding iodine nutrition status of pregnant women with SH are available. This study aimed to clarify whether iodine deficiency or excess is associated with SH, especially, when test results for anti-thyroid autoantibodies are negative.
  
  
  METHODS
  A total of 115 women with SH and 104 women with euthyroidism (EH) in early pregnancy in Tianjin, China were investigated, and their serum thyroid-stimulating hormone, free thyroxine, free triiodothyronine, anti-thyroid peroxidase antibody (TPOAb), anti-thyroid globulin antibody (TGAb), urinary iodine (UIC), and urinary creatinine (UCr) concentrations were measured. Thyroid ultrasonography was performed to determine thyroid echogenicity and volume. The UIC, UIC/UCr ratio, prevalence of TPOAb and TGAb positivity, and thyroid gland volume were compared between the EH and SH groups. UIC and ultrasonographic features were analysed in subjects in the SH group who were negative for TPOAb and TGAb.
  
  
  RESULTS
  Median UIC of SH (154.0 μg/L) and EH (150.1 μg/L) met the World Health Organization criterion for iodine sufficiency in pregnant women. Neither UIC nor the UIC/UCr ratio differed significantly between groups. The prevalence of TPOAb and TGAb positivity in the SH group was significantly higher than that in the EH group (P < 0.01). The percentage of subjects with UIC ≥ 250 μg/L in the SH group was significantly higher than that in the EH group (p = 0.004). The percentage of subjects negative for autoantibodies and UIC ≥ 250 μg/L in the SH group tended to be higher than that in subjects in the EH group negative for autoantibodies, but the difference was not statistically significant (p = 0.025, adjusted test level α = 0.0167). Eight of 18 subjects in the SH group with negative results for TPOAb and TGAb were diagnosed with Hashimoto thyroiditis by means of thyroid ultrasonography.
  
  
  CONCLUSIONS
  Women in early pregnancy with SH in Tianjin were iodine sufficient, but still at risk of iodine deficiency as pregnancy progressed. UIC ≥ 250 μg/L was associated with increased risk of SH. Serological negative autoimmune thyroiditis and UIC ≥ 250 μg/L may play a role in pathogenesis of SH cases with negative results for autoantibodies.
authors.affiliation: Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China.
authors.forename: Kunling
authors.initials: K
authors.lastname: Wang
authors.affiliation: Department of Surgery, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China.
authors.forename: Fengao
authors.initials: F
authors.lastname: Li
authors.affiliation: Department of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, 300070, China.
authors.forename: Wanqi
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China.
authors.forename: Li
authors.initials: L
authors.lastname: Ding
authors.affiliation: Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China.
authors.forename: Yaxin
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Key Lab of Hormone and Development, Institute of Endocrinology, Tianjin Medical University, Tianjin, 300070, China.
authors.forename: Laixiang
authors.initials: L
authors.lastname: Lin
authors.affiliation: Project Office, Tianjin Women's and Children's Health Center, No96 Guizhou Road, Heping District, Tianjin, 300070, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Endocrinology and Metabolism, Tianjin Medical University General Hospital, No154 Anshan Road, Heping District, Tianjin, 300052, China. meichuqin@163.com.
authors.forename: Mei
authors.initials: M
authors.lastname: Zhu
mesh_terms: D000328:Adult; D002681:China / Q000453:epidemiology; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000473:pathology*; D007455:Iodine / Q000652:urine*; D011247:Pregnancy; D015995:Prevalence; D013960:Thyroid Function Tests; D014463:Ultrasonography
chemical_list: D007455:Iodine
keywords: Anti-thyroid globulin antibody (TPOAb); Anti-thyroid peroxidase antibody (TPOAb); Early pregnancy; Idiopathic subclinical hypothyroidism; Subclinical hypothyroidism; Urine iodine concentration