title: First trimester isolated maternal hypothyroxinaemia: adverse maternal metabolic profile and impact on the obstetrical outcome.
abstract: BACKGROUND
  Isolated maternal hypothyroxinaemia (IH) is defined as low maternal FT4 (<5th percentile) and normal thyroid-stimulating hormone. There is concern on its potential negative effects on the mother and offspring.
  
  
  OBJECTIVE
  We aimed to evaluate the prevalence of IH and to assess the consequences of hypothyroxinaemia on the maternal and foetal outcomes.
  
  
  METHODS
  From a total of 1300 consecutive pregnant women recruited during the prenatal screen (mean gestational age, 11·8 weeks), thyroid function parameters were assessed in 879 women. After exclusion of women with T4 supplements, with twin pregnancies and with diabetes, data from 783 women were included. Maternal and neonatal outcomes in 55 selected women with IH and negative thyroid auto-antibodies without thyroid disorders or pregnancy achieved through assisted reproductive techniques were compared with a selected euthyroid control group (N = 165).
  
  
  RESULTS
  Among the 783 non diabetic singleton pregnant women, 68 women (8·7%) were identified with IH. When compared to the selected euthyroid controls, selected women with hypothyroxinaemia had significantly increased body mass index (BMI) in preconception (P = 0·003), in the first trimester (P = 0·004) and at the time of delivery (P = 0·001). At term, foetal breech presentation and caesarean section rate were significantly higher (P = 0·006 and P = 0·026, respectively) than in the euthyroid controls. A significant increase in macrosomia was also noted (P = 0·026).
  
  
  CONCLUSIONS
  The prevalence of hypothyroxinaemia in early pregnancy was of 8·7%. IH is associated with an increased maternal BMI and is related with a risk of breech presentation, a significant increase in macrosomia and caesarean sections. Screening should consider overweight as risk factor for hypothyroxinaemia.
authors.affiliation: Department of Endocrinology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: Raluca M
authors.initials: RM
authors.lastname: Furnica
authors.affiliation: Department of Clinical Biology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: Damien
authors.initials: D
authors.lastname: Gruson
authors.affiliation: Institute of Molecular and Experimental Medicine, University Hospital of Wales, Cardiff University, Cardiff, UK.
authors.forename: John H
authors.initials: JH
authors.lastname: Lazarus
authors.affiliation: Department of Endocrinology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: Dominique
authors.initials: D
authors.lastname: Maiter
authors.affiliation: Department of Obstetrics, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Bernard
authors.affiliation: Department of Endocrinology, Université catholique de Louvain, Cliniques Universitaires Saint-Luc, Brussels, Belgium.
authors.forename: Chantal
authors.identifier: http://orcid.org/0000-0001-5706-0504
authors.initials: C
authors.lastname: Daumerie
mesh_terms: D000328:Adult; D015992:Body Mass Index; D001946:Breech Presentation; D002585:Cesarean Section; D005260:Female; D005320:Fetal Macrosomia; D006801:Humans; D009035:Mothers; D011247:Pregnancy; D011256:Pregnancy Outcome; D011261:Pregnancy Trimester, First / Q000097:blood*; D012189:Retrospective Studies; D013974:Thyroxine / Q000097:blood*; D055815:Young Adult
chemical_list: D013974:Thyroxine