How the thyroid gland can affect your menstrual cycle and chances of pregnancy

Your thyroid may be small, but it has a surprisingly big influence on your body. This butterfly-shaped gland sits at the front of your neck and produces hormones that help regulate everything from your metabolism and body temperature to your energy levels. It also plays an important role in your reproductive system.

If your thyroid gland isn’t producing the right amount of hormones, you might notice changes to your menstrual cycle, ovulation, and fertility. The good news? Thyroid conditions are usually straightforward to diagnose with a blood test and can be treated effectively.

Here’s what you need to know.

Key takeaways

• Your thyroid gland helps regulate your menstrual cycle, ovulation, and fertility.
• Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can affect your periods and make it harder to become pregnant.
• Thyroid conditions are usually diagnosed with a simple blood test.
• For many people, treating the underlying thyroid condition helps restore regular ovulation and improves fertility.

What does your thyroid actually do?

Your thyroid is a small gland in the front of your neck that produces two hormones called thyroxine (T4) and triiodothyronine (T3). These hormones act a bit like your body’s thermostat and control center. They help regulate energy use, heart rate, digestion, body temperature, and many other everyday functions. They’re also closely connected to your reproductive hormones.

Healthy thyroid hormone levels help support:

• Regular ovulation
• Healthy egg development
• Estrogen and progesterone production
• Preparation of the uterine lining for pregnancy
• Early embryo development

Because all of these systems work together, changes in thyroid hormone levels can sometimes affect your menstrual cycle and fertility.

Can thyroid problems affect your menstrual cycle?

Yes. When your thyroid isn’t producing the right amount of hormones, the delicate balance between your brain, ovaries, and uterus can be disrupted.

Depending on the type of thyroid condition you have, you might notice:

• Irregular periods
• Heavier or lighter bleeding
• Missed periods
• Changes in cycle length

Of course, a thyroid disease isn’t the only cause of these symptoms. Conditions like polyendocrine metabolic ovarian syndrome (PMOS), previously known as polycystic ovary syndrome (PCOS), stress, significant weight changes, and other hormonal conditions can also affect your menstrual cycle. But if you’ve noticed persistent changes to your periods, it’s worth speaking to your doctor.

Hypothyroidism: When your thyroid is underactive

Hypothyroidism means your thyroid gland isn’t producing enough thyroid hormones. Because your body’s systems slow down, symptoms often develop gradually and can be easy to overlook at first.

Symptoms of hypothyroidism

Some of the most common symptoms include:

• Fatigue or low energy
• Difficulty concentrating or “brain fog”
• Unusual sensitivity to cold
• Dry skin or brittle hair and nails
• Constipation
• Weight gain
• Muscle aches
• Heavy or irregular periods

Not everyone experiences every symptom, and many of these symptoms can have other causes too.

Can hypothyroidism affect fertility?

It can. Ovulation relies on a carefully balanced mix of hormones, and low thyroid hormone levels can sometimes disrupt that balance. This may make ovulation less regular, which can make it difficult to get pregnant.

The reassuring news is that many people with hypothyroidism conceive naturally, particularly once the condition has been diagnosed and treated. If you’re trying to conceive and have hypothyroidism, your doctor will usually monitor your thyroid hormone levels closely before and during pregnancy.

Hyperthyroidism: When your thyroid is overactive

Hyperthyroidism is the opposite condition. It happens when your thyroid produces too much thyroid hormone. Instead of slowing the body down, excess thyroid hormone speeds up many of the hormonal processes.

Symptoms of hyperthyroidism

Some common symptoms you might notice:

• Anxiety or irritability
• Heart palpitations
• Unexplained weight loss
• Unusual sensitivity to heat
• Trembling hands
• Lighter or less frequent periods
• Difficulty sleeping

Again, these symptoms can have many different causes, so it’s important not to self-diagnose but to ask your doctor.

Can hyperthyroidism affect fertility?

Yes. When thyroid hormone levels are too high, ovulation may happen less regularly or stop altogether, making pregnancy more difficult.

Untreated hyperthyroidism can also increase the risk of complications during pregnancy. The good news is that treatment helps restore normal thyroid function and improve fertility.

When should you speak to your doctor?

It’s worth making an appointment if:

• Your periods have become much heavier, lighter, or more irregular.
• You’ve stopped having periods, and you’re not pregnant.
• You’re experiencing symptoms and aren’t sure why.
• You’ve been trying to conceive for 12 months (or six months if you’re over 35).
• You’re trying to conceive and have a known thyroid condition.

A simple blood test by your doctor measuring thyroid hormones, including thyroid-stimulating hormone (TSH), is often enough to identify whether your thyroid gland could be contributing to your symptoms.

The bottom line

Your thyroid and reproductive hormones work closely together, so it’s not surprising that thyroid conditions can sometimes affect your menstrual cycle and fertility.

The important thing to remember is that thyroid conditions are common but mostly treatable. If you’re noticing changes to your periods, have any of the symptoms mentioned above, or you’re finding it difficult to conceive, speaking to your doctor is a good place to start. The doctor can arrange the right tests and, if needed, recommend treatment to help get your thyroid hormones back into balance.