title: Influences of perinatal factors on cord blood thyroid-stimulating hormone level.
abstract: BACKGROUND
  Cord blood thyroid-stimulating hormone level is affected by various perinatal factors. The aim of this study is to investigate the relative impact of these factors on the cord blood thyroid-stimulating hormone results in singleton pregnancies.
  
  
  METHODS
  The study group consisted of 20,086 consecutive singleton deliveries over a 3 year period. The effect of mode of delivery, infant sex, gestation at birth, birth weight, and duration of labor on the incidence of false elevation of cord blood thyroid-stimulating hormone was assessed by univariate analysis and logistic regression.
  
  
  RESULTS
  There was an independent positive association between false elevation of cord blood thyroid-stimulating hormone (> or =15.0 mIU/L) and birth weight (p=0.005), male infant sex (p<0.001), and instrumental delivery (p<0.001). Both elective and emergency cesarean section were negatively associated with elevated cord thyroid-stimulating hormone level (p<0.001). When the cutoff level was raised to 40.0 mIU/L, none of the variables examined were significant. The incidence of false positive tests (> or =15.0 mIU/L) was higher in neonates born by cesarean section for failed instrumental delivery and fetal distress than for failure to progress of labor (34.7% vs 4.5% vs 1.3% respectively, p<0.001).
  
  
  CONCLUSIONS
  While the incidence of false positive screening was significantly affected by various perinatal factors when the thyroid-stimulating hormone cutoff level is low, it was unaffected at a high cutoff level. The present study also provides further evidence that cord blood thyroid-stimulating hormone level reflects fetal response to perinatal stress events.
authors.affiliation: Department of Obstetrics and Gynaecology, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong, ROC. lyschan@netvigator.com
authors.forename: L Y
authors.initials: LY
authors.lastname: Chan
authors.forename: T N
authors.initials: TN
authors.lastname: Leung
authors.forename: T K
authors.initials: TK
authors.lastname: Lau
mesh_terms: D001724:Birth Weight; D036861:Delivery, Obstetric; D005189:False Positive Reactions; D005260:Female; D005312:Fetal Blood / Q000378:metabolism*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn / Q000502:physiology*; D007743:Labor, Obstetric; D016015:Logistic Models; D008297:Male; D011247:Pregnancy; D012189:Retrospective Studies; D012737:Sex Factors; D013972:Thyrotropin / Q000097:blood*
chemical_list: D013972:Thyrotropin