title: Challenges in the evaluation of urinary iodine status in pregnancy: the importance of iodine supplement intake and time of sampling.
abstract: OBJECTIVE
  Median urinary iodine concentration (UIC) is the recommended method to evaluate iodine status in pregnancy, but several factors may challenge the interpretation of the results. We evaluated UIC in pregnant women according to (1) sampling in the hospital versus at home, (2) time of the most recent iodine supplement intake prior to sampling, and (3) members of their household.
  
  
  METHODS
  Danish cross-sectional study in the year 2012. Pregnant women (n = 158), their male partners (n = 157) and children (n = 51) provided a questionnaire with detailed information on iodine supplement intake and a spot urine sample obtained in the hospital and/or at home for measurement of UIC and urinary creatinine concentration.
  
  
  RESULTS
  In the pregnant women providing a urine sample both in the hospital and at home (n = 66), individual UIC (p = 0.002) and urinary creatinine concentration (p = 0.042), but not estimated 24-hour urinary iodine excretion (p = 0.79), were higher when sampling was at home. Median UIC was dependent on the time of the most recent iodine supplement intake prior to sampling [same day (n = 79): 150 µg/l (95% CI 131-181 µg/l), the day before (n = 51): 105 µg/l (78-131 µg/l), several days ago/non-user (n = 28): 70 µg/l (56-94 µg/l), p < 0.001]. The pattern was similar in the male partners. Apart from a more frequent iodine supplement intake in pregnancy (87.3% vs. partners 15.9%), no systematic differences were observed in urinary measurements between the pregnant women and their partners.
  
  
  CONCLUSIONS
  Time of spot urine sampling and time span from iodine supplement intake to spot urine sampling should be considered when evaluating urinary iodine status in pregnancy.
authors.affiliation: Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark ; Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Stine Linding
authors.initials: SL
authors.lastname: Andersen
authors.affiliation: Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Louise Kolding
authors.initials: LK
authors.lastname: Sørensen
authors.affiliation: Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark ; Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Anne
authors.initials: A
authors.lastname: Krejbjerg
authors.affiliation: Department of Obstetrics and Gynecology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Margrethe
authors.initials: M
authors.lastname: Møller
authors.affiliation: Department of Endocrinology, Aalborg University Hospital, Aalborg, Denmark ; Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
keywords: 24-Hour urinary iodine excretion; Household; Iodine supplement; Pregnancy; Urinary creatinine concentration; Urinary iodine concentration