The thyroid gland plays a crucial role in regulating metabolism, energy, and hormonal balance throughout the body. What many people do not realise is that thyroid disorders can significantly impact fertility in both women and men. Thyroid dysfunction is one of the most common – and most treatable – causes of reproductive problems.
How the Thyroid Affects Reproduction
Thyroid hormones (T3 and T4) influence nearly every cell in the body, including the ovaries and testes. They play a direct role in regulating menstrual cycles and ovulation, supporting early pregnancy and foetal brain development, maintaining hormonal balance (including oestrogen and progesterone), and supporting normal sperm production in men.
Hypothyroidism (Underactive Thyroid)
Hypothyroidism is the most common thyroid disorder affecting fertility. When thyroid hormone levels are too low, women may experience irregular or heavy periods, anovulation (failure to ovulate), elevated prolactin levels (which further disrupts ovulation), increased risk of miscarriage, and complications during pregnancy including preeclampsia and preterm birth.
Hyperthyroidism (Overactive Thyroid)
An overactive thyroid can also disrupt fertility by causing light or irregular periods, difficulty conceiving, and increased risk of early pregnancy loss. Uncontrolled hyperthyroidism during pregnancy poses risks to both mother and baby.
Subclinical Hypothyroidism
This is a milder form where thyroid hormone levels are still within normal range, but TSH (thyroid-stimulating hormone) is slightly elevated. Even this subtle imbalance can affect fertility and increase miscarriage risk. Most fertility specialists recommend treating subclinical hypothyroidism in women trying to conceive, aiming for a TSH level below 2.5 mIU/L.
Thyroid and IVF
Thyroid function is routinely checked before starting IVF. Untreated thyroid disorders can reduce the response to ovarian stimulation, lower implantation rates, and increase miscarriage risk after embryo transfer. Optimising thyroid levels before and during IVF treatment is essential for the best outcomes.
Treatment
The treatment for hypothyroidism is straightforward – thyroid hormone replacement medication (levothyroxine) taken daily. With proper treatment and monitoring, most women with thyroid disorders can conceive and have healthy pregnancies. Regular blood tests ensure hormone levels remain optimal throughout the fertility journey and pregnancy.
If you are trying to conceive or planning fertility treatment, make sure your thyroid has been checked. A simple blood test can identify a problem that is easily correctable – and treating it can make a significant difference in your fertility outcomes.