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Objective: To establish the correlation of maternal urine iodine and neonatal thyroid stimulating hormone (TSH)
in iodine supplemented and non-iodine supplemented pregnant women.
Methods: The study was a prospective, randomized, controlled trial, which was conducted at the
antenatal care unit, labor ward, and neonatal unit of Siriraj Hospital, Mahidol University, Bangkok, Thailand. In
all, 224 pregnant women were recruited during 1 October 2015 and 31 July 2017. They were randomized into 2
groups: an iodine and a non-iodine supplemented group. One woman in the control group left the study as she
had delivery at another hospital.
Results: There were no statistically significant differences in the demographic data, original area of domicile, and
adverse neonatal outcomes (including preterm labor and low birth weight) of the patients in the two groups. The
maternal urinary iodine levels were 84.14 ± 61.85 and 58.41 ± 41.36 microgram/L, and the median values of the
neonatal TSH levels were 3.7 ± 1.87 and 4.4 ± 1.99 mIU/ml, in the iodine and non-iodine supplemented groups,
respectively. The differences in both values were statistically significant (p-value < 0.05).
Conclusion: This study determined that there were statistically significant differences in the maternal urinary iodine
levels and the median values of the neonatal TSH levels of the iodine and non-iodine replacement groups of pregnant
women. Even though there were no clinically significant differences and none of the newborns was diagnosed with
hypothyroidism, iodine supplementation in all pregnant women should be considered. A larger prospective, RCT
trial would confirm the benefits of a strategy of routinely administering iodine to pregnant women at Siriraj Hospital.
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