Material and Method: The present study was a prospective randomized controlled trial (RCT) that was taken at ANC unit, labor ward, and neonatal unit at Siriraj Hospital, Mahidol University, Bangkok, Thailand. Two hundred sixty six pregnant women were recruited between June 15, 2015 and July 31, 2016. They were randomized into two groups, iodine and no-iodine supplemented group.

Results: No statistical significant of demographic data, original habitant areas, and adverse neonatal outcomes including preterm labor and low birthweight, of the pregnant patient between these two groups. Only the median value of neonatal TSH level was 3.44 and 3.95 mIU/l in iodine and no-iodine supplemented group, respectively, which was statistically significant different between the two groups (p-value <0.05). However, there were no clinical difference between the two groups.

Conclusion: The present study presented that there was statistical significant difference of the median value of neonatal TSH level between two groups of iodine and no-iodine supplement pregnant women. Even if there was no clinically significant difference and none of the newborn was diagnosed of hypothyroidism, iodine supplementation in all pregnant women should be of concerned. A large prospective study would benefit the iodine implementation of pregnant women in Siriraj Hospital.

Keywords: Iodine supplementation, Neonatal TSH, Hypothyroidism