Thyroid disorders are more common than many people realise — and they can affect fertility, pregnancy outcomes and the health of both mother and baby.
Why thyroid health matters for fertility
The thyroid produces hormones that regulate metabolism, energy and reproduction. Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid) can disrupt ovulation, menstrual cycles and fertility.
Hypothyroidism can cause irregular or absent periods, making conception harder. Even mild hypothyroidism (subclinical) has been associated with reduced fertility and higher miscarriage risk.
Hyperthyroidism, particularly Graves’ disease, can also disrupt ovulation and increase the risk of miscarriage, preterm birth and low birth weight.
Should you test before trying to conceive?
Yes — if you have symptoms of thyroid dysfunction, a family history of thyroid disease, or have been diagnosed with a thyroid condition, testing before pregnancy is strongly recommended.
The standard tests are:
- TSH — the first-line screening test
- Free T4 — confirms hormone levels
- Anti-TPO antibodies — identifies autoimmune thyroid disease (Hashimoto’s)
For women with known thyroid disease, TSH should be checked before conception and monitored closely during pregnancy, as hormone requirements often increase.
How thyroid treatment affects fertility
Levothyroxine (for hypothyroidism) is safe in pregnancy and often the dose needs to be increased by 20–30% once pregnancy is confirmed. Well-controlled hypothyroidism supports normal ovulation and reduces miscarriage risk.
Antithyroid medications (for hyperthyroidism) require careful management during pregnancy. Some medications are preferred over others, and doses may need adjustment. Radioactive iodine treatment must be completed well before conception.
The bottom line
Thyroid disorders are common, treatable, and important to address before pregnancy. If you are planning to conceive and have any thyroid symptoms or risk factors, a simple blood test can provide answers — and treatment can significantly improve your chances of a healthy pregnancy.
This article is for educational purposes only. Always consult a qualified healthcare professional about your specific situation.