No Association Was Found Between Mild Iodine Deficiency During Pregnancy and Pregnancy Outcomes: a Follow-up Study Based on a Birth Registry

Background Severe iodine deficiency during gestation is associated with adverse pregnancy outcomes; however, the impact of mild-to-moderate iodine deficiency, though prevalent in pregnancy, remains unclear. Methods We extracted follow-up data for 7435 pregnant women from a national iodine deficiency disorders monitoring program from 2016 to 2018 and a mother–child cohort study in 2017 based on a birth registry in Shanghai. Birth outcomes were collected from the registry. Spot urine and household salt samples were collected for iodine testing. Single-factor analysis and logistic regression were used to evaluate the association between maternal iodine status and pregnancy outcomes. Results The median urine iodine level in pregnant women was 137.5 μg/L (interquartile range 82.4–211.5), suggesting mild deficiency according to WHO standards. The incidence of pregnancy termination, preterm birth, congenital malformations, low birth weight, and cesarean section was 3.2%, 4.3%, 1.4%, 2.7%, and 45.2% in the mildly iodine-deficient group and 3.4%, 4.5%, 1.4%, 2.7%, and 44.5% in the normal group, respectively. After adjusting for maternal age and education, trimesters, and preterm birth rate in the general population, the odds ratios for any outcome did not differ significantly between the two groups. Conclusion The present study suggests that mild maternal iodine deficiency is not associated with adverse pregnancy outcomes.