How Thyroid Health Affects Your Period and Fertility

It’s easy to overlook the thyroid, after all, it’s small, silent, and doesn’t exactly call attention to itself. But when it comes to your menstrual cycle and fertility, it plays a surprisingly big role.

Whether you’ve been dealing with irregular periods, struggling to conceive, or just feeling off and can’t explain why, it might be time to consider your thyroid health.

What Is the Thyroid, and What Does It Do?

Your thyroid is a butterfly-shaped gland that sits at the base of your neck. It produces hormones that regulate your metabolism, basically, how your body uses energy. But thyroid hormones also affect your heart rate, mood, digestion, body temperature, and yes, your reproductive system.

The two most common thyroid conditions are:

• Hypothyroidism: When your thyroid is underactive and produces too little hormone.

• Hyperthyroidism: When it’s overactive and produces too much hormone.

Both can interfere with your menstrual cycle and fertility in different ways.

How Thyroid Issues Affect Your Menstrual Cycle

Thyroid hormones work closely with reproductive hormones like estrogen and progesterone. When the thyroid isn’t functioning properly, this delicate balance can get disrupted.

If You Have Hypothyroidism:

• Periods may become heavier or longer than usual.

• You might experience irregular cycles, or even missed periods.

• You could notice fatigue, weight gain, dry skin, constipation, or feeling unusually cold.

If You Have Hyperthyroidism:

• Periods might become lighter, shorter, or even disappear for a time.

• You may have frequent cycles or feel like your body is “on edge” hormonally.

• Other symptoms can include weight loss, anxiety, a fast heartbeat, insomnia, or sweating more than usual.

Because these symptoms can overlap with other issues, like PCOS, perimenopause, or stress, it’s common for thyroid problems to go unnoticed for a while.

The Thyroid–Fertility Connection

Your body is smart. If it senses that hormone levels are out of sync, it may put reproduction on the back burner. That’s why untreated thyroid disorders can make it harder to conceive.

How Hypothyroidism Can Affect Fertility:

• Ovulation may be delayed or not happen at all.

• The uterine lining might not develop as it should, making implantation more difficult.

• There’s also a higher risk of miscarriage in early pregnancy if thyroid levels are low.

How Hyperthyroidism Can Affect Fertility:

• It may disrupt ovulation or shorten the luteal phase (the second half of your cycle).

• Some people experience hormonal imbalance that prevents successful implantation.

• It can also lead to pregnancy complications if not treated beforehand.

What About Autoimmune Thyroid Disorders?

Two autoimmune conditions often linked to thyroid issues are:

• Hashimoto’s thyroiditis – the most common cause of hypothyroidism.

• Graves’ disease – the most common cause of hyperthyroidism.

Autoimmune conditions can add another layer of complexity. They don’t just affect thyroid function, they may also increase the risk of early pregnancy loss or affect egg quality. But with proper management, many people with autoimmune thyroid disorders go on to have healthy pregnancies.

When to Get Your Thyroid Checked

If you’re experiencing any of the following, it’s worth asking your GP for a simple blood test (usually TSH, T3, and T4 levels):

• Irregular or absent periods

• Unexplained fatigue or weight changes

• Hair thinning or brittle nails

• Difficulty getting pregnant

• History of miscarriage or complications

• A family history of thyroid disease

Testing is straightforward, and treatment, whether it’s medication or further investigation, is often effective and accessible.

Treatment and Next Steps

• Hypothyroidism is usually treated with a daily tablet of levothyroxine, a synthetic version of the hormone your body isn’t producing enough of.

• Hyperthyroidism may be managed with antithyroid medications, radioiodine treatment, or (in some cases) surgery.

If you're trying to conceive, your thyroid levels may need to be kept within a tighter range than usual. It’s also important to continue monitoring thyroid function throughout pregnancy, as hormone needs often change during that time.

Your thyroid may be small, but its impact on your reproductive health is significant. If something doesn’t feel right with your cycle, or if you’re trying to get pregnant and it’s taking longer than expected, thyroid testing is a simple step that could offer clarity.

The sooner a thyroid issue is identified, the sooner it can be treated, and that can make all the difference in your fertility journey and overall well-being.