Insufficient iodine nutrition status and the risk of pre-eclampsia: a systemic review and meta-analysis

Abstract

BackgroundAlthough subclinical hypothyroidism in pregnancy is one of the established risk factors for pre-eclampsia, the link between iodine deficiency, the main cause of hypothyroidism, and pre-eclampsia remains uncertain. We conducted a systematic review to determine the iodine nutrition status of pregnant women with and without pre-eclampsia and the risk of pre-eclampsia due to iodine deficiency.MethodsMEDLINE, EMBASE, Google Scholar, Scopus and Africa-Wide Information were searched up to 30th June 2020. Random-effect model meta-analysis was used to pool mean difference in urinary iodine concentration (UIC) between pre-eclamptic and normotensive controls and pool ORs and incidence rates of pre-eclampsia among women with UIC <150 µg/L.ResultsFive eligible studies were included in the meta-analysis. There was a significant difference in the pooled mean UIC of 254 pre-eclamptic women and 210 normotensive controls enrolled in three eligible case–control studies (mean UIC 164.4 µg/L (95% CI 45.1 to 283.6, p<0.01, I2 >50)). The overall proportions of pre-eclampsia among women with UIC <150 µg/L and UIC >150 µg/L in two cross-sectional studies were 203/214 and 67/247, respectively, with a pooled OR of 0.01 (95% CI 0 to 4.23, p=0.14, I2 >50) for pre-eclampsia among women with UIC >150 µg/L. The overall incidence of pre-eclampsia among women with UIC <150 µg/L and UIC >150 µg/L in two cohort studies was 6/1411 and 3/2478, respectively, with a pooled risk ratio of 2.85 (95% CI 0.42 to 20.05, p=0.09, I2 <25).ConclusionAlthough pre-eclamptic women seem to have lower UIC than normotensive pregnant women, the available data are insufficient to provide a conclusive answer on association of iodine deficiency with pre-eclampsia risk.PROSPERO registration numberCRD42018099427.

Iodine deficiency in pregnancy along a concentration gradient is associated with increased severity of preeclampsia in rural Eastern Cape, South Africa

“…These findings correlate with previous case-control studies that reported a positive association between insufficient iodine intake and preeclampsia [ 12 , 30 , 31 ]. A recent systematic review found a significant difference in the mean UIC of preeclamptic and normotensive pregnant controls but no increased risk of preeclampsia among pregnant women with UIC < 150 μg/L in the included cohort studies [ 32 ]. The study was, however, limited by the very few numbers of included studies and high heterogeneity across studies.…”

“…Differences in the findings between these studies and ours could partly be accounted for by the timing of the iodine and thyroid function tests. While the iodine and thyroid function status in our study were measured in the third trimester, the cohort studies in the systematic review [ 32 ], as well as the study by Richie et al [ 33 ], estimated the risk of preeclampsia based only on the iodine and thyroid function status estimates in the first trimester. This approach did not consider the impact of the iodine nutritional state in the second half of pregnancy on the risk of preeclampsia.…”

Iodine supplementation: compliance and association with adverse obstetric and neonatal outcomes

“…A recent meta-analysis in euthyroid women showed that the pooled prevalence of preterm birth, low birth weight and hypertensive disorders were not associated with first trimester urinary iodine levels ( 31 ). Another systematic review and meta-analysis suggested that even though pre-eclamptic women presented lower urinary iodine levels, additional studies are needed to conclude on the association with iodine deficiency ( 32 ). Interestingly, in a Norwegian cohort study, iodine supplement use initiated before pregnancy reduced the risk of preeclampsia but not that of other measured adverse outcomes; this study did not address miscarriages ( 33 ).…”