Maternal iodine insufficiency and adverse pregnancy outcomes

This study aimed to assess the iodine status of pregnant women in each trimester and to compare the pregnancy outcomes between groups with iodine insufficiency and iodine sufficiency. Longitudinal study on urinary iodine concentration (UIC) in each trimester as well as comparison between women with iodine insufficiency (<150mcgL(-1)) and iodine sufficiency was conducted. Pregnant women without thyroid diseases who had not received iodine supplementation were recruited for UIC measurements in each trimester and were followed up for pregnancy outcomes. In the analysis of 384, 325 and 221 samples in the first, second and third trimester, the medians of UICs were 147.39, 157.01 and 153.07mcgL(-1), respectively. Of 399 women, 174 (43.6%) had a UIC less than 150mcgL(-1) (suggesting iodine insufficiency) and 225 (56.4%) had a UIC greater than or equal to 150mcgL(-1) (suggesting iodine sufficiency). Of 390 women with availability of the final outcomes, 171 and 219 in the insufficiency and sufficiency group, respectively, the rates of preterm birth and low birthweight were significantly higher in the insufficiency group, 17.5% vs. 10.0% (P=0.031) and 19.9% vs. 12.3% (P=0.042), respectively. Logistic regression analysis showed that iodine status was an independent risk of preterm birth and low birthweight. Finally, women with a UIC<100mcgL(-1) had a significantly higher rate of fetal growth restriction, 13/68 vs. 30/322 (P=0.031). In northern Thailand, a great number of pregnant women had a median UIC less than 150mcgL(-1) and they had a higher risk of preterm birth and low birthweight. Finally, those with a median UIC of less than 100 mcgL(-1) had a higher risk of fetal growth restriction.