title: Maternal thyroid dysfunction during gestation, preterm delivery, and birthweight. The Infancia y Medio Ambiente Cohort, Spain.
abstract: BACKGROUND
  Maternal clinical thyroid disorders can cause reproductive complications. However, the effects of mild thyroid dysfunctions are not yet well established. The aim was to evaluate the association of maternal thyroid function during the first half of pregnancy with birthweight and preterm delivery.
  
  
  METHODS
  We analysed data on 2170 pregnant women and their children from a prospective population-based cohort study in four Spanish areas. Mid-gestation maternal serum and urine samples were gathered to determine thyroid-stimulating hormone (TSH), free thyroxine (fT4 ), and urinary iodine concentration (UIC). Thyroid status was defined according to percentile distribution as: euthyroid (TSH and fT4 >5th and <95th percentiles); hypothyroxinaemia (fT4  < 5 th percentile and TSH normal), hypothyroidism (TSH > 95th percentile and fT4 normal or <5th percentile), hyperthyroxinaemia (fT4  > 95 th percentile and TSH normal), and hyperthyroidism (TSH < 5 th percentile and fT4 normal or >95th percentile). Response variables were birthweight, small and large for gestational age (SGA/LGA), and preterm delivery.
  
  
  RESULTS
  An inverse association of fT4 and TSH with birthweight was found, the former remaining when restricted to euthyroid women. High fT4 levels were also associated with an increased risk of SGA [odds ratio, 95% confidence interval (CI) 1.28 (95% CI 1.08, 1.51)]. Mean birthweight was higher in the hypothyroxinaemic group (β = 109, P < 0.01). Iodine intake and UIC were not associated with birth outcomes.
  
  
  CONCLUSIONS
  High maternal fT4 levels during the first half of pregnancy were related to lower birthweight and increased risk of SGA newborns, suggesting that maternal thyroid function may affect fetal growth, even within the normal range.
authors.affiliation: Pharmacy, University Cardenal Herrera-CEU, Valencia, Spain.
authors.forename: Gemma
authors.initials: G
authors.lastname: León
authors.forename: Mario
authors.initials: M
authors.lastname: Murcia
authors.forename: Marisa
authors.initials: M
authors.lastname: Rebagliato
authors.forename: Mar
authors.initials: M
authors.lastname: Álvarez-Pedrerol
authors.forename: Ane M
authors.initials: AM
authors.lastname: Castilla
authors.forename: Mikel
authors.initials: M
authors.lastname: Basterrechea
authors.forename: Carmen
authors.initials: C
authors.lastname: Iñiguez
authors.forename: Ana
authors.initials: A
authors.lastname: Fernández-Somoano
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Blarduni
authors.forename: Carles M
authors.initials: CM
authors.lastname: Foradada
authors.forename: Adonina
authors.initials: A
authors.lastname: Tardón
authors.forename: Jesús
authors.initials: J
authors.lastname: Vioque
mesh_terms: D000328:Adult; D001724:Birth Weight / Q000502:physiology*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007037:Hypothyroidism / Q000097:blood* / Q000150:complications / Q000453:epidemiology / Q000503:physiopathology; D007231:Infant, Newborn; D007455:Iodine / Q000097:blood; D009035:Mothers; D016017:Odds Ratio; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology* / Q000209:etiology; D011297:Prenatal Exposure Delayed Effects / Q000097:blood*; D011446:Prospective Studies; D013030:Spain / Q000453:epidemiology; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D013972:Thyrotropin; D007455:Iodine; D013974:Thyroxine
keywords: birthweight; iodine; maternal thyroid dysfunction; preterm birth; thyroid hormones