The Joint Role of Iodine Status and Thyroid Function on Risk for Preeclampsia in Finnish Women: a Population-Based Nested Case-Control Study

Abstract

Preeclampsia, a pregnancy disorder that includes hypertension and proteinuria, is a major cause of maternal and fetal morbidity and mortality. Some studies, but not all, have found that women with preeclampsia have significantly lower iodine levels than healthy pregnant women. Resolving this issue is important because iodine deficiency in pregnancy is common in the USA and parts of Europe including Finland. We conducted a nested case-control study to determine whether the risk for preeclampsia is associated with iodine status. We measured serum iodine, thyroglobulin (Tg), and thyroid stimulating hormone (TSH) at 10-14 weeks gestational age in 204 women with preeclampsia and 246 unaffected controls selected from all births in Finland. We found no significant difference in iodine (case mean = 26.04 ng/mL, control mean = 27.88 ng/mL, p = 0.995), Tg (case mean = 31.11 ng/mL, control mean = 29.61 ng/mL, p = 0.996), and TSH (case mean = 1.30 mIU/L, control mean = 1.24 mIU/L, p = 0.896) levels between cases and controls. There was no significant relationship between preeclampsia risk and iodine, Tg, or TSH after adjustment for known risk factors. These results are reassuring given the high prevalence of iodine deficiency in pregnancy.

Urinary iodine as an important indicator for preeclampsia: a Polish perspective

“…A study by Reische et al [22], however, showed no significant difference in iodine levels (case mean = 26.04 ng/ mL, control mean = 27.88 ng/mL, p=0.995) between preeclamptic and healthy women. There was also no significant difference in the TSH levels between compared groups (case mean = 1.30 mIU/L, control mean = 1.24 mIU/L, p=0.896).…”

“…There are many controversial results in the literature regarding the relationship between UIC and the risk of PE. Some of the studies reported lower iodine levels in women with PE compared to healthy pregnant women [19][20][21], while other studies show opposite results [9,22]. Iodine deficiency is very common among pregnant women in many European countries, as well as in the USA [23], therefore it is necessary to verify the possible relationship between the iodine level and the risk of PE.…”

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

“…The study was, however, limited by the very few numbers of included studies and high heterogeneity across studies. Reische et al [ 33 ] in a recent case-control study using nationally representative data from Finland reported no difference in serum iodine, TSH and other thyroid parameters of preeclamptic and normotensive pregnant women. Differences in the findings between these studies and ours could partly be accounted for by the timing of the iodine and thyroid function tests.…”

“…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.…”

Genetically determined thyroid disease and risk of preeclampsia : a Mendelian Randomization study

“…[9] . However, a nested case-control study showed no signi cant correlation between TSH levels and preeclampsia [10] . In addition, hypothyroidism and hypothyroxinemia were not linked to hypertensive disorders, but hyperthyroidism was linked to a higher chance of developing hypertension [11] .…”