Hypothyroidism & Fertility

What is hypothyroidism?

Hypothyroidism means the thyroid gland in the neck does not make enough thyroid hormone. Thyroid hormone controls the body's metabolism and also influences the reproductive system. In overt hypothyroidism, thyroid hormone (free T4) is low and TSH is high. In subclinical hypothyroidism, TSH is raised but T4 is still normal. Thyroid problems are common in women of reproductive age, including in India, and both types can affect fertility and pregnancy.

Symptoms and signs

• Tiredness, sluggishness and feeling cold
• Weight gain and puffiness of the face
• Dry skin, hair loss and brittle nails
• Constipation
• Low mood and poor concentration
• Heavy, irregular or infrequent periods
• Difficulty conceiving or miscarriage
• A swelling in the neck (goitre)

Subclinical hypothyroidism often causes no symptoms and is found on a blood test.

Causes and risk factors

• Autoimmune thyroiditis (Hashimoto's thyroiditis), the most common cause
• Iodine deficiency in some regions
• Previous thyroid surgery or radioactive iodine treatment
• Some medicines, such as lithium and amiodarone
• Family history of thyroid disease or other autoimmune conditions such as type 1 diabetes

How it affects fertility

Low thyroid hormone can disturb ovulation, cause irregular periods and raise prolactin levels, which further interferes with ovulation. Untreated hypothyroidism is linked with a higher risk of miscarriage, preterm birth and effects on the baby's development. Thyroid antibodies (anti-TPO) are also associated with a higher risk of miscarriage even when thyroid levels are normal.

How it is diagnosed

• TSH blood test, the main screening test
• Free T4 to distinguish overt from subclinical hypothyroidism
• Anti-TPO antibodies to check for autoimmune thyroiditis
• Prolactin, as it may be raised in hypothyroidism
• Thyroid ultrasound if a goitre or nodule is found

Treatment options

Levothyroxine

Hypothyroidism is treated with a daily levothyroxine tablet, taken on an empty stomach. The dose is adjusted based on TSH tests every 4 to 6 weeks until stable. For women trying to conceive or having fertility treatment, many specialists aim to keep TSH below 2.5 mIU/L. Treatment of subclinical hypothyroidism is commonly advised for women trying to conceive when TSH is above the reference range.

During pregnancy

The need for thyroid hormone rises in early pregnancy. Women already on levothyroxine usually need a dose increase as soon as pregnancy is confirmed, and TSH should be checked regularly throughout pregnancy.

Fertility treatment if needed

Once thyroid levels are normal, many women ovulate regularly again. If pregnancy still does not happen, further fertility tests and treatments such as ovulation induction, IUI or IVF may be considered depending on other findings.

Chances of pregnancy

When hypothyroidism is well controlled, the chances of conceiving and having a healthy pregnancy are generally similar to those of women without thyroid disease, though other fertility factors and age still matter. Outcomes vary, and no treatment can guarantee pregnancy.

When to see a fertility specialist

See a specialist if you have hypothyroidism and have been trying for 12 months (6 months if 35 or older), if your periods are irregular, or if you have had a miscarriage. All women planning pregnancy with known thyroid disease should have their TSH checked before conceiving. Iswarya Fertility offers fertility evaluation at its 91+ centres.