• Charles Jonathan Peter Snart, Diane Erin Threapleton, Claire Keeble, Elizabeth Taylor, Dagmar Waiblinger, Stephen Reid, Nisreen A Alwan, Dan Mason, Rafaq Azad, Janet Elizabeth Cade, Simpson Nigel A B NAB Division of Women's and Children's Health, School of Medicine, University of Leeds, Leeds, LS2 9JT, UK., Sarah Meadows, Amanda McKillion, Gillian Santorelli, Amanda H Waterman, Michael Zimmermann, Paul M Stewart, John Wright, Mark Mon-Williams, Darren Charles Greenwood, and Laura J Hardie.
• Leeds Institute of Cardiovascular & Metabolic Medicine, LIGHT Laboratories, School of Medicine, University of Leeds, Leeds, LS2 9JT, UK.
• Bmc Med. 2020 Jun 11; 18 (1): 132.

BackgroundSevere iodine insufficiency in pregnancy has significant consequences, but there is inadequate evidence to indicate what constitutes mild or moderate insufficiency, in terms of observed detrimental effects on pregnancy or birth outcomes. A limited number of studies have examined iodine status and birth outcomes, finding inconsistent evidence for specific outcomes.MethodsMaternal iodine status was estimated from spot urine samples collected at 26-28 weeks' gestation from 6971 mothers in the Born in Bradford birth cohort. Associations with outcomes were examined for both urinary iodine concentration (UIC) and iodine-to-creatinine ratio (I:Cr). Outcomes assessed included customised birthweight (primary outcome), birthweight, small for gestational age (SGA), low birthweight, head circumference and APGAR score.ResultsThere was a small positive association between I:Cr and birthweight in adjusted analyses. For a typical participant, the predicted birthweight centile at the 25th percentile of I:Cr (59 μg/g) was 2.7 percentage points lower than that at the 75th percentile of I:Cr (121 μg/g) (99% confidence interval (CI) 0.8 to 4.6), birthweight was predicted to be 41 g lower (99% CI 13 to 69) and the predicted probability of SGA was 1.9 percentage points higher (99% CI 0.0 to 3.7). There was no evidence of associations using UIC or other birth outcomes, including stillbirth, preterm birth, ultrasound growth measures or congenital anomalies.ConclusionLower maternal iodine status was associated with lower birthweight and greater probability of SGA. Whilst small, the effect size for lower iodine on birthweight is comparable to environmental tobacco smoke exposure. Iodine insufficiency is avoidable, and strategies to avoid deficiency in women of reproductive age should be considered.Trial RegistrationClinicalTrials.gov NCT03552341. Registered on June 11, 2018.

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