Thyroid function and autoimmunity in Danish pregnant women after an iodine fortification program and associations with obstetric outcomes

Abstract

Objective: Aberrations in maternal thyroid function and autoimmunity during pregnancy have been associated with negative obstetric outcome. In Denmark, a national iodine fortification program was implemented in the year 2000 with the aim to alleviate the mild-moderate iodine deficiency. Following the iodine implementation, there has been an increase in thyroid autoimmunity in the background population. This study investigates the thyroid status of pregnant Danish women following the iodine fortification program, and a possible association with preterm delivery. Design: Historical cohort study of 1278 randomly selected pregnant Danish women attending the national Down's syndrome screening program. Methods: The main outcome measures were thyroid status according to laboratory-and gestational-age-specific reference intervals, and association with risk of abnormal obstetric outcome. Antibody-positivity was defined as an antibody-level (thyroid peroxidase and/or thyroglobulin antibodies) above 60 U/ml. Results: Establishing laboratory-specific gestational-age-dependent reference intervals, we found a prevalence of maternal thyroid dysfunction of 10%-15.8% by use of the cut-off suggested by the American Thyroid Association. Thyroid dysfunction was significantly associated with antibody-positivity (P!0.05). No associations were found between preterm delivery and thyroid dysfunction (adjusted OR 0.6, 95% CI: 0.1-2.3) or autoimmunity (adjusted OR 1.1, 95% CI: 0.4-2.7). Conclusions: After the implementation of the Danish iodine fortification program, the prevalence of thyroid dysfunction and autoimmunity in Danish pregnant women is high -even higher by use of pre-established reference intervals from international consensus guidelines. However, no associations were found with abnormal obstetric outcome. Large randomized controlled trials are needed to clarify the benefit of treating slight aberrations in pregnant women's thyroid function.

Prevalence of thyroid autoimmunity and dysfunction in women with iron deficiency during early pregnancy: is it altered?

“…In a more recent paper, the cross-reactivity hypothesis could however not be confirmed (23). Data on the prevalence of TAI in pregnant women after iodine fortification (like the fortification program in Denmark) taught us that the prevalence of TAI increased 10 years later (24). In Belgium, however, attempts to increase the daily iodine intake are not opposed by the authorities and are still voluntary.…”

Maternal thyroid parameters in pregnant women with different ethnic backgrounds: Do ethnicity‐specific reference ranges improve the diagnosis of subclinical hypothyroidism?

“…e.g. in Denmark) taught us that its prevalence increased 10 years later . In Belgium however, attempts to increase the daily iodine intake have not been implemented by the authorities and are still voluntary.…”

Comparison of thyroglobulin and thyroid peroxidase antibodies measured by five different kits in autoimmune thyroid diseases

“…Therefore, we searched for recent reports on screening studies of TgAb and TPOAb. To avoid the influence of diseases themselves, we only considered studies done on healthy control subjects in various regions in different countries [24][25][26][27][28][29][30][31][32][33][34][35][36][37]. In healthy subjects, the incidence of positive TgAb or TPOAb is …”