Newborn Iodine Status Is Not Related to Congenital Hypothyroidism.
BACKGROUND
Severe iodine deficiency or excess during pregnancy can cause congenital hypothyroidism (CH). Iodine deficiency is common in pregnant women in the United States.


OBJECTIVES
We conducted a nested case-control study in a cohort of ∼2.5 million births in California to determine whether iodine status is related to CH in a US population.


METHODS
Dried blood spots from 907 newborns with CH identified by newborn screening and 909 unaffected controls matched by month of birth were obtained from the California Newborn Screening Program to measure whole-blood iodine concentration. Iodine status was compared between cases and controls, and logistic regression was used to assess the association between CH status and blood iodine concentrations. Iodine status was also compared between cases and controls among infants treated in a neonatal intensive care unit (NICU) because CH has been reported in infants exposed to high levels of iodine in the NICU.


RESULTS
Blood iodine concentrations did not differ significantly between cases (median: 20.0 ng/mL; IQR: 12.1-29.8 ng/mL) and controls (median: 20.3 ng/mL; IQR: 12.5-30.9 ng/mL; P = 0.59). Neither extremely high nor extremely low blood iodine concentrations (1st, 5th, 95th, and 99th percentiles of the distribution) were more common in cases. Among infants treated in NICUs, however, cases had significantly (P = 0.01) higher iodine (median: 22.7 ng/mL; IQR: 16.4-32.1 ng/mL) compared with controls (median: 17.3 ng/mL; IQR: 8.3-26.6 ng/mL).


CONCLUSIONS
CH cases did not have significantly higher or lower iodine in this population, which is reassuring given that maternal iodine deficiency is common in the United States. Among newborns in the NICU, CH cases had higher blood iodine concentrations compared with controls, suggesting that excess iodine exposure in the NICU could be causing CH. It may be beneficial to monitor iodine exposure from surgical procedures, imaging, and iodine-containing disinfectants and to consider non-iodine alternatives.
['Mills|James L|JL|', 'Reische|Elijah C|EC|', 'Kannan|Kurunthachalam|K|', 'Gao|Chongjing|C|', 'Shaw|Gary M|GM|', 'Sundaram|Rajeshwari|R|']
D016022:Case-Control Studies D003409:Congenital Hypothyroidism D059788:Dried Blood Spot Testing D005260:Female D006801:Humans D007231:Infant, Newborn D007455:Iodine D008297:Male D015997:Neonatal Screening D011247:Pregnancy
iodine congenital hypothyroidism iodine deficiency pregnancy newborn screening NICU iodine exposure Wolff–Chaikoff effect iodine excess