Thyroid autoimmunity and iron deficiency in pregnancy

Thyroid autoimmunity and iron deficiency are both common in pregnancy, posing a risk for numerous adverse fetal and maternal outcomes, including miscarriage. A clinical study just published in the European Journal of Endocrinology the important connection between thyroid autoimmunity and low iron, both of which can be recognized at an early stage. The authors state:

"Thyroid disorders and iron deficiency (ID) are associated with obstetrical and fetal complications. Iron is essential for the normal functioning of thyroid peroxidase (TPO-abs) and ID is frequent during pregnancy. The aim of this study was to compare the prevalence of thyroid autoimmunity (TAI) and dysfunction during the first trimester of pregnancy in women with and without ID."

They measured ferritin to determine iron status, TPO-abs (thyroid peroxidase antibodies) for thyroid autoimmunity, and thyroid-stimulating hormone (TSH) and free T₄ (FT₄) thyroid function. Note that their definitions for iron deficiency (ID) and thyroid autoimmunity (TAI) were extremely 'generous' with ID defined as ferritin <15µg/L and TAI as TPO-abs >60kIU/L. Practitioners in this country should also note their definition of subclinical hypothyroidism (SCH) as TSH was >2.5mIU/L.

Thyroid autoimmunity and iron deficiency are common

Their data also demonstrated a significant coupling between the two:

"ID was present in 35% of women. Age and BMI were comparable between both groups. In the ID group, the prevalence of TAI and SCH was significantly higher, compared with that in the non-ID group (10% vs 6% and 20% vs 16% respectively). Ferritin was inversely correlated with serum TSH and positive with FT₄ levels. In the logistic regression model, ID remained associated with TAI after correction for confounding factors. The association with SCH was absent after correction for the confounders in the logistic regression model, but remained present in the linear regression model."

Medscape Medical News comments on these findings:

"While previous studies have indicated that iron deficiency during pregnancy can affect from 24% to 44% of women, this is the first to show the secondary effect of an increased prevalence of thyroid autoimmunity."

Thyroid autoimmunity poses serious maternal and fetal risks. Also stated in Medscape:

"Senior author Kris G Poppe, MD, PhD, head of the Endocrine Clinic, University Hospital CHU St-Pierre, Brussels, Belgium, told Medscape Medical News that this finding is important because thyroid autoimmunity in pregnant women increases the risk of miscarriage, preterm delivery, and low birth weight compared with unaffected women."

For important points on the multiple adverse affects of thyroid autoimmunity on pregnancy and the neonate see the earlier post Subclinical hypothyroidism in pregnancy. Standard of care for pregnancy planning and management should always include testing ferritin, thyroid antibodies and function.The authors conclude:

"ID was frequent during the first trimester of pregnancy and was associated with a higher prevalence of TAI, higher serum TSH, and lower FT₄levels."