Iodine is an essential macronutrient for feto-maternal growth and development. Emerging evidence suggests that maternal iodine deficiency during pregnancy is potentially associated with both maternal and fetal adverse outcomes. The aim of this systematic review and meta-analysis was to investigate the association between maternal iodine status in euthyroid pregnant women and adverse pregnancy outcomes. A comprehensive literature search was performed in PubMed, Web of Science and Scopus up to October 2019 for retrieving related published articles in English. World Health Organization maternal median urinary iodine concentration (UIC) classification was used as follows: median UIC of less than 100, 100-149, 150-249, and more than 250 μg/L, for moderate-to-severe iodine deficiency, mild iodine deficiency, iodine adequate and more than adequate-to-excessive iodine, respectively. The primary outcomes of interest in this meta-analysis were the pooled prevalence and pooled odds ratio of the preterm birth, low birth weight (LBW), and one composite outcome of hypertensive disorders of pregnancy comprising pregnancy hypertension and preeclampsia. The secondary outcome was pooled mean of neonatal characteristics including birth weight, head circumference, Apgar score, and gestational age at birth. A total of 6 studies involving 7698 participants were included in this meta-analysis. The pooled prevalence of preterm birth, LBW, and hypertensive disorders of pregnancy were not statistically significantly different in the four groups of UIC levels. The pooled prevalence of preterm birth was 0.05, 0.04, 0.04, and 0.03 in UIC < 100, 100-149, 150-249, and > 250 μg/L, respectively. No evidence of an association was observed among the odds of preterm birth, LBW, and hypertensive disorders of pregnancy in euthyroid pregnant women with UIC between 100 and 149, 150-249, and > 250 μg/L compared with UCI < 100 μg/L. Likewise, there were not any statistical significant differences between the neonatal characteristics in different UIC groups. The results remained unchanged after subgroup analysis based on UIC less than 150 μg/L as abnormal UIC level. The present meta-analysis showed that the UIC of euthyroid pregnant women is not generally associated with the pregnancy outcomes and it per se is an insufficient indicator for prediction of pregnancy complications. The results of this study are important for reproductive healthcare providers and policymakers in providing appropriate healthcare service for pregnant women. However, further studies are needed to confirm these findings.
Keywords: Adverse pregnancy outcome; Meta-analysis; Urinary iodine concentration.