Thyroid disorders in subfertility and early pregnancy

Abstract

Disorders of thyroid function are common in pregnancy and have implications for foetal and maternal health. Thyroid autoimmunity, as evidenced by the presence of elevated levels of anti-thyroid antibodies (anti-TPO and anti-Tg antibodies) is associated with an increased risk of miscarriage, though the mechanism remains poorly understood. There has been considerable focus on the implications and optimal management of pregnant women with thyroid disease, especially those undergoing assisted reproduction. Pregnancy results in significant changes in thyroid physiology and these need to be understood by clinicians involved in the care of pregnant women. Guidelines for the use of thyroxine and target thyroid function tests have been produced by international bodies but it is recognised that these predominantly reflect expert opinion rather than established evidence-based practice. Importantly a number of key clinical trials have been performed to aid understanding, particularly of the consequences of hypothyroidism for mother and baby, and the effectiveness of thyroid hormone use in autoimmune and subclinical hypothyroidism. This review summarises the current knowledge base and guidance for practice relating to thyroid disorders in pregnancy and subfertility.

Keywords: autoimmune disease; hyperthyroidism; hypothyroidism; pregnancy; subclinical hyperthyroidism; subclinical hypothyroidism; thyroid auto-antibody.

Figure 1.

Forest plot illustrating the comparison of spontaneous abortion rates between treated and nontreated subclinical hypothyroid women from the controlled clinical trials described in Tables 2 and 3. The meta-analysis indicates no benefit on rate of spontaneous abortions with treatment.

Figure 2.

Forest plot illustrating the comparison of preterm delivery rates between treated and nontreated subclinical hypothyroid women from the controlled clinical trials described in Tables 2 and 3 The meta-analysis indicates a reduction of preterm delivery rates in treated subclinical hypothyroidism.

Figure 3.

Forest plot illustrating the comparison of low birth weights between treated and nontreated subclinical hypothyroid women from the clinical trials described in Tables 2 and 3. The meta-analysis indicates no impact of treatment on low birth weight.

Figure 4.

Forest plot illustration the comparative rates of IUGR between treated and nontreated subclinical hypothyroid women from the clinical trials described in Tables 2 and 3. The meta-analysis indicates no impact on rate of IUGR with treatment in women with subclinical hypothyroidism. IUGR, intrauterine growth restriction.

Proposed algorithm for assessment and management of thyroid disease in the pre-conception period or early pregnancy based on the information gathered in this review article. Key learning points - Screening for thyroid dysfunction should be considered in all those who have a previous personal or family history of thyroid dysfunction, if there are ongoing symptoms of thyroid dysfunction, in those with a past medical history of other autoimmune conditions (e.g. type 1 diabetes mellitus), as part of infertility investigations and recurrent miscarriage history and those with previous head and neck irradiation. - Ensure free thyroid hormone levels are measured and in cases of multiple pregnancy, hyperemesis, and trophoblastic disease interpret results with caution. - Ensure trimester-specific reference ranges are used. - Consider the need for iodine supplementation in all pregnant patients. - Thyroid antibodies may indicate a risk of miscarriage; however, if thyroid function is within trimester-specific reference ranges there are currently no data suggesting benefit of levothyroxine supplementation.