title: Women with high early pregnancy urinary iodine levels have an increased risk of hyperthyroid newborns: the population-based Generation R Study.
abstract: OBJECTIVE
  Iodine deficiency during pregnancy results in thyroid dysfunction and has been associated with adverse obstetric and foetal effects, leading to worldwide salt iodization programmes. As nowadays 69% of the world's population lives in iodine-sufficient regions, we investigated the effects of variation in iodine status on maternal and foetal thyroid (dys)function in an iodine-sufficient population.
  
  
  METHODS
  Urinary iodine, serum TSH, free T4 (FT4) and TPO-antibody levels were determined in early pregnancy (13·3 (1·9) week; mean (SD)) in 1098 women from the population-based Generation R Study. Newborn cord serum TSH and FT4 levels were determined at birth.
  
  
  RESULTS
  The median urinary iodine level was 222·5 μg/l, indicating an iodine-sufficient population. 30·8% and 11·5% had urinary iodine levels <150 and >500 μg/l, respectively. When comparing mothers with urinary iodine levels <150 vs ≥150 μg/l, and >500 vs ≤500 μg/l, there were no differences in the risk of maternal increased or decreased TSH, hypothyroxinaemia or hyperthyroidism. Mothers with urinary iodine levels >500 μg/l had a higher risk of a newborn with decreased cord TSH levels (5·6 ± 1·4 (mean ± SE) vs 2·1 ± 0·5%, P = 0·04), as well as a higher risk of a hyperthyroid newborn (3·1 ± 0·9 vs 0·6 ± 0·3%, P = 0·02). These mothers had newborns with higher cord FT4 levels (21·7 ± 0·3 vs 21·0 ± 0·1 pm, P = 0·04). Maternal urinary iodine levels <150 μg/l were not associated with newborn thyroid dysfunction.
  
  
  CONCLUSIONS
  In an iodine-sufficient population, higher maternal urinary iodine levels are associated with an increased risk of a hyperthyroid newborn.
authors.affiliation: The Generation R Study Group, Erasmus Medical Center, The Netherlands; Department of Internal Medicine, Erasmus Medical Center, The Netherlands.
authors.forename: Marco
authors.initials: M
authors.lastname: Medici
authors.forename: Akhgar
authors.initials: A
authors.lastname: Ghassabian
authors.forename: Willy
authors.initials: W
authors.lastname: Visser
authors.forename: Sabine M P F
authors.initials: SM
authors.lastname: de Muinck Keizer-Schrama
authors.forename: Vincent W V
authors.initials: VW
authors.lastname: Jaddoe
authors.forename: W Edward
authors.initials: WE
authors.lastname: Visser
authors.forename: Herbert
authors.initials: H
authors.lastname: Hooijkaas
authors.forename: Albert
authors.initials: A
authors.lastname: Hofman
authors.forename: Eric A P
authors.initials: EA
authors.lastname: Steegers
authors.forename: Jacoba J
authors.initials: JJ
authors.lastname: Bongers-Schokking
authors.forename: H Alec
authors.initials: HA
authors.lastname: Ross
authors.forename: Henning
authors.initials: H
authors.lastname: Tiemeier
authors.forename: Theo J
authors.initials: TJ
authors.lastname: Visser
authors.forename: Yolanda B
authors.initials: YB
authors.lastname: de Rijke
authors.forename: Robin P
authors.initials: RP
authors.lastname: Peeters
mesh_terms: D005260:Female; D005312:Fetal Blood; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood*; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000097:blood*; D007454:Iodides; D007455:Iodine / Q000652:urine*; D009035:Mothers; D011247:Pregnancy; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D007454:Iodides; D013972:Thyrotropin; D007455:Iodine; D013974:Thyroxine