From the Guidelines
Managing thyroid disorders in individuals with infertility or pregnancy complications requires careful monitoring and treatment, with levothyroxine being the treatment of choice for hypothyroidism and propylthiouracil and methimazole for hyperthyroidism, to minimize risks of miscarriage, preterm birth, and neurodevelopmental issues in offspring. The goal of treatment is to maintain TSH levels between 0.1-2.5 mIU/L for optimal fertility and pregnancy outcomes, as evidenced by studies such as 1. For women with pre-existing hypothyroidism, a 30-50% increase in their levothyroxine dose during pregnancy is often necessary, typically beginning as soon as pregnancy is confirmed, as noted in 1. Key considerations in managing thyroid disorders during pregnancy include:
- Monitoring thyroid function every 4-6 weeks, with medication adjustments as needed, to prevent adverse outcomes such as miscarriage and preterm birth, as discussed in 1
- Using propylthiouracil in the first trimester and methimazole in the second and third trimesters for hyperthyroidism, due to the lower risk of birth defects associated with these medications, as recommended in 1
- Treating subclinical hypothyroidism with levothyroxine to improve conception rates and prevent adverse pregnancy outcomes, as suggested by 1
- Reassessing thyroid function postpartum, as medication requirements typically return to pre-pregnancy levels, to ensure ongoing management of thyroid disorders and prevention of long-term complications, as noted in 1. Overall, careful management of thyroid disorders is crucial to minimize risks and ensure optimal outcomes for individuals with infertility or pregnancy complications, as emphasized by the evidence from 1.
From the FDA Drug Label
For pregnant patients with pre-existing hypothyroidism, measure serum TSH and free-T4 as soon as pregnancy is confirmed and, at minimum, during each trimester of pregnancy. In pregnant patients with primary hypothyroidism, maintain serum TSH in the trimester-specific reference range The recommended daily dosage of levothyroxine sodium tablets in pregnant patients is described in Table 3. Inform patients to promptly report symptoms that may be associated with vasculitis including new rash, hematuria or decreased urine output, dyspnea or hemoptysis Because methimazole may cause hypoprothrombinemia and bleeding, prothrombin time should be monitored during therapy with the drug, especially before surgical procedures. Thyroid function tests should be monitored periodically during therapy Once clinical evidence of hyperthyroidism has resolved, the finding of a rising serum TSH indicates that a lower maintenance dose of methimazole should be employed.
Management of Thyroid Disorders in Individuals with Infertility or Pregnancy Complications:
- Hypothyroidism: The goal is to maintain serum TSH in the trimester-specific reference range. The recommended daily dosage of levothyroxine sodium tablets in pregnant patients is based on the patient population and starting dosage, with dose adjustments and titration as needed.
- Hyperthyroidism: Methimazole is used to treat hyperthyroidism, but it may cause hypoprothrombinemia and bleeding, so prothrombin time should be monitored during therapy. Thyroid function tests should be monitored periodically during therapy.
- Key Considerations:
- Monitor serum TSH and free-T4 levels in pregnant patients with hypothyroidism.
- Adjust levothyroxine sodium dosage as needed to maintain serum TSH in the trimester-specific reference range.
- Monitor thyroid function tests periodically during methimazole therapy.
- Be aware of the potential risks of methimazole use during pregnancy, particularly in the first trimester.
- Consider alternative anti-thyroid medications, such as propylthiouracil, for pregnant women requiring treatment for hyperthyroidism, especially in the first trimester 2 3.
From the Research
Thyroid Disorders and Infertility
- Thyroid disorders can affect fertility and fetal development, making it essential to manage them properly in individuals with infertility or pregnancy complications 4, 5.
- Hyperthyroidism and hypothyroidism are common thyroid disorders that can impact fertility, with hyperthyroidism affecting approximately 0.2% to 1.4% of people worldwide and hypothyroidism being a common cause of infertility in women 5, 6.
Management of Thyroid Disorders
- The management of thyroid disorders in individuals with infertility or pregnancy complications involves assessing and treating the underlying condition, as well as monitoring thyroid function tests and adjusting treatment as needed 4, 7.
- Treatment options for hyperthyroidism include antithyroid drugs, radioactive iodine ablation, and surgery, while treatment for hypothyroidism typically involves levothyroxine replacement therapy 7, 6.
- In cases of subclinical hyperthyroidism or hypothyroidism, treatment may not always be necessary, and the decision to treat should be individualized based on the patient's symptoms, thyroid function tests, and overall health status 5, 6.
Infertility Diagnosis and Treatment
- Infertility is defined as the failure to achieve pregnancy after 12 months of regular unprotected sexual intercourse, and approximately 85% of infertile couples have an identifiable cause 8.
- The most common causes of infertility are ovulatory dysfunction, male factor infertility, and tubal disease, and treatment options may include ovulation induction, intrauterine insemination, or in vitro fertilization (IVF) 8.
- Thyroid disorders can be a contributing factor to infertility, and treating the underlying thyroid condition may improve fertility outcomes 5.
Pregnancy Complications
- Thyroid disorders can also impact pregnancy outcomes, with untreated hyperthyroidism or hypothyroidism increasing the risk of adverse pregnancy outcomes such as miscarriage, preterm birth, and low birth weight 4, 6.
- Proper management of thyroid disorders during pregnancy is essential to minimize the risk of pregnancy complications and ensure the best possible outcomes for both the mother and the fetus 4.