Iodine intakes of pregnant females from Québec, Canada.

Background: Adequate maternal iodine intake is important for fetal brain development. Based on iodine intakes of non-pregnant females of reproductive age from the Canadian Health Measures Survey (2016 -2017) it can be extrapolated that most pregnant females in Canada will not meet iodine requirements without supplementation.

Objectives: To assess iodine intakes of 500 pregnant, nulliparous females from Québec, Canada and report on use of multivitamin/mineral (MVM) supplements and coverage of iodized salt.

Methods: Duplicate spot urine samples were collected at 10.1 -14.9 weeks (T1) and 19.7 -24.9 weeks (T2) of gestation. Median urinary iodine concentrations (UIC) were compared with WHO/UNICEF/ICCIDD reference ranges. Daily iodine intakes were calculated from UIC using a formula that corrects for urine dilution using creatinine and accounts for urinary iodine excretion rate. Usual (adjusted for within-person variation) iodine intakes were estimated from duplicate daily intake measurements (T1 and T2 measures) using the National Cancer Institute method. Prevalence of inadequate or excessive intakes were determined from usual intakes by the Estimated Average Requirement (EAR) or Tolerable Upper Intake Level (UL) cut-point method, respectively.

Results: Females (median: 30.1 years) were mostly white race (94.4 %), highly educated and consumed iodized salt (92 %). Median UIC at T1 (136 µg/L, IQR: 71 -230) was lower (p<0.001) than at T2 (193 µg/L, IQR: 112 -390). Almost all females used a MVM supplement (98.2 %) with 35.6 % starting supplementation preconception and 0.6 %, 28.4 %, 19.8 %, 7.2 % and 6.0 % starting 1 -2 weeks, 3 -4 weeks, 5 -8 weeks, 8 -12 weeks and > 12 weeks postconception, respectively. Almost all (99 %, 95 % CI: 98, 100) had usual iodine intakes ≥EAR and ≤UL.

Conclusions: Prevalence of inadequate or excessive usual iodine intakes was low. However, about two-thirds of females started MVM supplementation postconception and median UIC at T1 was below the adequate range of 150 -249 µg/L.