Raphael Jagroep1, Joris Osinga1, Irwin Reiss2, Robin Peeters1, Tim Korevaar1
(1) Internal Medicine, Erasmus MC, Rotterdam, Netherlands.
(2) Neonatology, Erasmus MC, Rotterdam, Netherlands.
Background
Thyroid dysfunction and iron deficiency (ID) are common in pregnancy, and both linked to adverse pregnancy outcomes. Iron is required for thyroperoxidase activity, and ID may contribute to the etiology of thyroid dysfunction. We aimed to assess the association of iron status with thyroid function during pregnancy.
Methods
We enrolled women from Generation R, a prospective birth study cohort, with at least one measurement for both iron status and thyroid function during pregnancy. We excluded non-live births, twin pregnancies, fertility treatment (IVF/ICSI), and prepregnancy thyroid disease/thyroid-altering medication usage. Multivariable linear or logistic regression models examined associations of ferritin, transferrin saturation, hemoglobin, or iron status groups (iron deficiency anemia (IDA), non-anemic ID, iron overload) with TSH and FT4, thyroid function test abnormalities, and TPOAb positivity.Results5,628 women were included, with 178 cases of IDA, 1,069 of non-anemic ID, and 306 of iron overload.Higher ferritin was associated with lower TSH (?:-0.0009 log TSH,[CI-0.0014;-0.0004],P=0.0006), but not with FT4. Higher transferrin saturation was associated with lower TSH (non-linear,P<=0.0001) and lower FT4 (non-linear,P=0.022). Higher hemoglobin was associated with higher FT4 (?:0.27,[CI0.16;0.38],P<=0.0001), but not TSH. The iron overload group had a 3.35-fold higher risk of overt hyperthyroidism ([CI1.24;9.07],P=0.018). Both the non-anemic ID, and the IDA groups had a higher risk of being TPOAb positive (OR2.06,[CI1.07 -3.95],P=0.03 and OR1.59,[CI1.17-2.16],P=0.003 respectively).
Interpretation
Lower iron status was associated with lower thyroid function and thyroid autoimmunity in pregnancy. These findings support treating non-anemic ID and suggest evaluating hypothyroidism symptoms in women with iron deficiency.