title: Subclinical hypothyroidism and pregnancy outcomes.
abstract: BACKGROUND
  Clinical thyroid dysfunction has been associated with pregnancy complications such as hypertension, preterm birth, low birth weight, placental abruption, and fetal death. The relationship between subclinical hypothyroidism and pregnancy outcomes has not been well studied. We undertook this prospective thyroid screening study to evaluate pregnancy outcomes in women with elevated thyrotropin (thyroid-stimulating hormone, TSH) and normal free thyroxine levels.
  
  
  METHODS
  All women who presented to Parkland Hospital for prenatal care between November 1, 2000, and April 14, 2003, had thyroid screening using a chemiluminescent TSH assay. Women with TSH values at or above the 97.5th percentile for gestational age at screening and with free thyroxine more than 0.680 ng/dL were retrospectively identified with subclinical hypothyroidism. Pregnancy outcomes were compared with those in pregnant women with normal TSH values between the 5th and 95th percentiles.
  
  
  RESULTS
  A total of 25,756 women underwent thyroid screening and were delivered of a singleton infant. There were 17,298 (67%) women enrolled for prenatal care at 20 weeks of gestation or less, and 404 (2.3%) of these were considered to have subclinical hypothyroidism. Pregnancies in women with subclinical hypothyroidism were 3 times more likely to be complicated by placental abruption (relative risk 3.0, 95% confidence interval 1.1-8.2). Preterm birth, defined as delivery at or before 34 weeks of gestation, was almost 2-fold higher in women with subclinical hypothyroidism (relative risk, 1.8, 95% confidence interval 1.1-2.9).
  
  
  CONCLUSIONS
  We speculate that the previously reported reduction in intelligence quotient of offspring of women with subclinical hypothyroidism may be related to the effects of prematurity.
  
  
  METHODS
  II-2.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9032, USA. brian.casey@utsouthwestern.edu
authors.forename: Brian M
authors.initials: BM
authors.lastname: Casey
authors.forename: Jodi S
authors.initials: JS
authors.lastname: Dashe
authors.forename: C Edward
authors.initials: CE
authors.lastname: Wells
authors.forename: Donald D
authors.initials: DD
authors.lastname: McIntire
authors.forename: William
authors.initials: W
authors.lastname: Byrd
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Leveno
authors.forename: F Gary
authors.initials: FG
authors.lastname: Cunningham
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D016001:Confidence Intervals; D005260:Female; D005500:Follow-Up Studies; D005865:Gestational Age; D006801:Humans; D007037:Hypothyroidism / Q000175:diagnosis* / Q000188:drug therapy; D007231:Infant, Newborn; D007234:Infant, Premature; D007752:Obstetric Labor, Premature; D011247:Pregnancy; D011248:Pregnancy Complications / Q000175:diagnosis*; D011256:Pregnancy Outcome; D011336:Probability; D012189:Retrospective Studies; D018570:Risk Assessment; D013960:Thyroid Function Tests; D013974:Thyroxine / Q000627:therapeutic use
chemical_list: D013974:Thyroxine