Thyroid and Fertility: Your Guide to TSH Levels for Getting Pregnant

Fertility isn’t separate from the rest of the body. The reproductive system is part of the endocrine system, which means it runs on hormones. The ovaries don’t just release eggs; they function as hormone producing glands, sending estrogen and progesterone into the bloodstream. Those hormones are in constant conversation with other hormone-regulating centers in the body, including the brain.

The thyroid is part of that hormone messenger system, and when it’s not functioning correctly, it can affect overall health and fertility. Here’s what the thyroid does and how it can influence reproduction.

What is the thyroid and why does it matter for fertility?

The thyroid is a butterfly-shaped gland located in your neck, just above your collarbone. Despite its size, the thyroid plays a pivotal role in the endocrine system. It influences metabolism, body temperature, heart rate, digestion, and more, which is why thyroid issues can show up in ways that feel random at first.

Here’s the basic pathway: the pituitary gland releases thyroid-stimulating hormone (TSH), which tells the thyroid how much triiodothyronine (T3) and thyroxine (T4) to produce. When the thyroid is functioning normally, it produces enough T3 and T4 to support the body’s core functions.

Now the fertility connection. TSH, T3, and T4 don’t operate in isolation. They interact with reproductive hormones, and when thyroid hormone levels are too high or too low, hormonal signaling in the reproductive system can get thrown off. As outlined in a 2021 study for Thyroid Research, thyroid hormones play a direct role in ovarian function, including follicle development and ovulation. That helps explain why thyroid dysfunction can disrupt cycles and make ovulation less predictable.

Research published in Best Practice & Research Clinical Endocrinology & Metabolism in 2020 found that even mild or subclinical thyroid dysfunction was associated with ovulatory disorders and reduced fertility, particularly in people trying to conceive.

Thyroid health also matters once conception happens. Adequate levels of T4 are critical in early pregnancy, before a developing embryo can make its own thyroid hormones. Research for Cureus in 2024 notes that untreated thyroid disorders are linked to higher risks of miscarriage and implantation failure, which is one reason thyroid testing is often part of fertility workups.

Does thyroid affect fertility?

Yes. Thyroid health affects fertility because thyroid hormones help regulate the hormonal choreography that supports ovulation, menstrual regularity, egg development, and implantation. When thyroid levels are out of range, even slightly, that choreography can fall out of sync.

Both hypothyroidism and hyperthyroidism can have a negative impact on fertility and increase the risk of miscarriage and premature birth, so it’s worth checking thyroid levels before TTC, especially if your cycles are irregular or you’ve had pregnancy loss.

One of the biggest pathways is cycle disruption. Thyroid hormones influence how the brain communicates with the ovaries. As Dr. Caledonia Buckheit, OB/GYN, explains: “Hypothyroidism, which leads to high levels of TRH and TSH, leads to elevated prolactin, this prolactin then shuts down GnRH pulsatility, which can lead to the loss of normal LH and FSH signalling.”

Thyroid hormones also affect egg development and the uterine lining. A 2020 study for JBRA Assisted Reproduction found that thyroid hormone receptors are present in both ovarian tissue and the uterine lining, which suggests a direct role in egg maturation and implantation.

The reassuring part is that thyroid related fertility issues are often treatable. Once thyroid levels are identified and properly managed, many people see improvements in cycle regularity, ovulation, and pregnancy outcomes.

TSH level to get pregnant: What's ideal?

If you’re trying to conceive, many reproductive endocrinologists aim for a TSH level below 2.5 mIU/L. That’s often lower than what’s considered “normal” for the general population, but pregnancy and fertility place extra demands on the thyroid.

Standard lab reference ranges for TSH often go up to around 4.0 or even 4.5 mIU/L. That might be fine if you’re not TTC, but fertility and early pregnancy are different. According to the American Endocrine Society, women trying to conceive or in early pregnancy are often advised to aim for a TSH below 2.5 mIU/L, particularly in the first trimester when the developing embryo relies on maternal thyroid hormone.

Research backs this up. A 2023 study for Human Reproduction Open found that women with subclinical hypothyroidism had higher miscarriage rates and lower live birth rates compared to those with TSH levels under 2.5 mIU/L. Even when thyroid hormone levels fall within the normal range, outcomes may be better when TSH is optimized for pregnancy.

This is why testing TSH before trying to conceive can be helpful. It gives you time to adjust levels proactively rather than reacting once you’re already pregnant. According to research for Cochrane Library published in 2015, identifying and treating thyroid dysfunction prior to pregnancy is associated with improved fertility and pregnancy outcomes.

If you’re adjusting medication or newly pregnant, monitoring matters. Many providers recheck TSH every 4 to 6 weeks during early pregnancy or when making medication changes, since levels can shift quickly.

Getting pregnant with hypothyroidism

When the thyroid doesn’t create and release enough thyroid hormone into your bloodstream, this is called hypothyroidism. Hypothyroidism can slow down your metabolism and can cause symptoms like fatigue, weight gain, constipation, and cold intolerance.

Hypothyroidism can also affect the menstrual cycle, including irregular periods and missed ovulation. A 2015 review for Clinical and Experimental Reproductive Medicine found thyroid dysfunction is associated with ovulatory disorders that can make getting pregnant more difficult.

The good news is that hypothyroidism is very treatable. With proper management, many people conceive and go on to have healthy pregnancies.

Hypothyroidism and infertility: The connection

When thyroid hormone levels are low, the ovaries may not respond properly to reproductive hormones like FSH and LH. This can interfere with the release of an egg from the ovary, reducing the chances of conception.

Hypothyroidism can also affect progesterone production during the second half of the cycle. Progesterone supports implantation and early pregnancy, so disruptions may make it harder for an embryo to implant successfully.

Untreated hypothyroidism is associated with a higher risk of miscarriage. According to research published in The Journal of Obstetrics and Gynecology of India in 2013, both overt and subclinical hypothyroidism increase the risk of pregnancy loss, particularly when TSH is elevated early on.

How to lower TSH levels to get pregnant

Levothyroxine replaces the thyroid hormone your body isn’t making enough of, which can lower TSH levels. It’s considered safe and effective for people trying to conceive and during pregnancy when monitored appropriately.

After starting or adjusting medication, TSH is often rechecked after about 4 to 6 weeks. It can take weeks to months to reach optimal levels for conception, which is why testing and treatment before TTC can be helpful.

Lifestyle factors like sleep, stress management, and addressing nutrient deficiencies can support thyroid health alongside treatment, but medication is the main lever when hypothyroidism is present.

Is it hard to get pregnant with hypothyroidism?

Without treatment, it can be more challenging. With proper care, many people with hypothyroidism conceive successfully. Staying consistent with medication, keeping up with blood tests, and working closely with your provider can make a meaningful difference.

Getting pregnant with hypothyroidism and PCOS

Getting pregnant with both hypothyroidism and PCOS can feel like a double whammy. These conditions can show up together, and thyroid issues are more common in people with PCOS than in the general population. Research published in Endocrine Connections in 2018 supports that link, and a 2023 review for Frontiers in Endocrinology suggests thyroid dysfunction may worsen the hormonal imbalances already present in PCOS.

Both conditions can affect ovulation, but in different ways. Hypothyroidism can disrupt brain to ovary signaling, while PCOS often involves excess androgens and insulin resistance that can prevent follicles from maturing and releasing an egg. When both are present, ovulation may be inconsistent, delayed, or not happen at all without treatment.

Treatment often means addressing both pieces: bringing TSH into a fertility supportive range, and supporting ovulation when needed. It can take longer and require more monitoring, but pregnancy is absolutely possible.

Can Hashimoto's cause infertility?

Hashimoto’s thyroiditis is an autoimmune condition where the immune system attacks the thyroid gland, often leading to hypothyroidism over time. With fertility, Hashimoto’s can matter even before thyroid hormone levels fall outside the normal range.

That’s because thyroid antibodies may affect fertility beyond just TSH. Many people with Hashimoto’s have elevated thyroid peroxidase (TPO) or thyroglobulin antibodies, and research links these antibodies to reduced fertility and higher miscarriage risk even when TSH, T3, and T4 are normal.

When TTC, treatment often focuses on keeping TSH in a fertility supportive range and monitoring thyroid status closely. According to a study for Endocrine Connections in 2013, careful monitoring and treatment of autoimmune thyroid disease before and during pregnancy can reduce miscarriage risk.

Thyroid and implantation failure

Thyroid antibodies may interfere with implantation by disrupting immune balance at the uterine level. A 2023 review for the International Journal of Molecular Sciences linked autoimmune thyroid disease with changes in immune signaling that can affect implantation and placental development.

Dr. Buckheit recommends: “Stick with the basics. Make sure your thyroid disease is well controlled, and maintain a healthy lifestyle including nutrient rich foods, adequate sleep and stress management.”

Does hyperthyroidism affect fertility?

Hyperthyroidism is an overactive thyroid, meaning the thyroid produces too much thyroxine (T4). It can speed up metabolism and cause symptoms like weight loss, increased appetite, anxiety, disrupted sleep, and lighter or irregular cycles.

Pregnancy is possible with hyperthyroidism, but going untreated can make conception harder and increase pregnancy risks. According to the British Thyroid Foundation, hyperthyroidism is associated with menstrual irregularities, ovulatory dysfunction, and reduced fertility when hormone levels remain uncontrolled.

Hyperthyroidism and infertility

Hyperthyroidism can disrupt luteinizing hormone and follicle stimulating hormone signaling, leading to missed ovulation or unpredictable timing. A review by the American Thyroid Association in 2022 notes that thyroid hormone imbalance can negatively affect ovarian function and follicular development.

Untreated hyperthyroidism is linked to increased risks of miscarriage, preterm birth, low birth weight, and pregnancy complications. Controlling thyroid levels before and during pregnancy significantly reduces these risks.

Hyperthyroidism and ovulation

Excess thyroid hormone increases sex hormone binding globulin levels and alters estrogen metabolism. This disrupts feedback loops between the brain and ovaries, which are essential for predictable ovulation.

When hormonal signaling is impaired, ovulation may not occur at all. Anovulatory cycles are more common in untreated hyperthyroidism, particularly when symptoms like weight loss and cycle changes are present.

Lighter, shorter, or irregular cycles are also common with hyperthyroidism. Without consistent cycle patterns, identifying fertile windows becomes harder, reducing the chances of timed conception.

Once thyroid hormone levels are brought back into range, ovulation often resumes. Treating hyperthyroidism improves cycle regularity and restores ovulatory function in many patients, improving fertility outcomes overall.

Graves’ disease and fertility

Graves’ disease is an autoimmune condition and the most common cause of hyperthyroidism. Graves’ disease can affect fertility through both high thyroid hormone levels and autoimmune activity.

Treatment may include antithyroid medications, and in some cases definitive treatment before pregnancy, but timing should be individualized to balance fertility goals with disease control. Providers often monitor antibody levels alongside thyroid hormones before and during pregnancy.

Hypothyroid and ovulation: What you need to know

Hypothyroidism can interfere with ovulation by altering brain to ovary signaling. Low thyroid hormone is also associated with increased prolactin levels, which can suppress the hormones needed to trigger ovulation.

After ovulation, progesterone supports the luteal phase and prepares the uterine lining for implantation. Hypothyroidism may reduce progesterone production by affecting corpus luteum function. A 1998 study for the Journal of Endocrinology noted thyroid hormones play a role in progesterone secretion, which helps explain why some people experience short or abnormal luteal phases.

BBT charting can sometimes offer clues. The British Thyroid Foundation notes that thyroid dysfunction can affect temperature regulation, and some people notice consistently low temperatures or a delayed post ovulation rise. BBT can’t diagnose thyroid disease, but patterns like these can be a nudge to get labs checked.

If you’re seeing irregular cycles, missed periods, inconsistent LH surges, short luteal phases, or trouble confirming ovulation, it may be worth exploring thyroid testing. Signs like fatigue, cold sensitivity, and unexplained weight changes alongside cycle changes can also point toward a thyroid issue.

How to lower TSH for fertility (and when you actually need to)

Higher TSH usually means lower thyroid function. It’s a signal that your brain is asking the thyroid to work harder because thyroid hormone levels are low.

For fertility, “normal” isn’t always optimal. While many labs accept TSH levels up to 4.0 or 4.5 mIU/L, the American Thyroid Association’s 2011 guidelines note that people trying to conceive are often advised to aim for a TSH below 2.5 mIU/L. Higher levels are linked to ovulation issues and increased miscarriage risk, though not everyone above this threshold needs treatment.

If treatment is needed, levothyroxine is the most effective way to lower TSH. Lifestyle and nutrition can support thyroid health, but they won’t replace medication when hypothyroidism is present. Don’t self medicate, megadose iodine, or rely on detoxes or supplements to “fix” TSH. These approaches can backfire.

Most providers recheck TSH every 4 to 6 weeks when adjusting treatment. The goal isn’t a perfect number, it’s supporting ovulation and early pregnancy safely.

How to lower thyroid levels to get pregnant

If your thyroid hormones T3 and T4 are too high, you’re dealing with hyperthyroidism. The goal is to lower thyroid hormone levels so ovulation and early pregnancy can happen safely.

Treating hyperthyroidism before TTC matters. The European Thyroid Association’s 2021 guidelines note that stabilizing thyroid levels prior to conception improves fertility and pregnancy outcomes.

Antithyroid medications are usually the first option. Methimazole and propylthiouracil (PTU) reduce thyroid hormone production, and treatment choice is individualized. Radioactive iodine is not safe when TTC or pregnant, and pregnancy is typically delayed at least 6 months after treatment. Surgery may be considered in specific cases.

Thyroid levels are often checked every 4 to 6 weeks while adjusting treatment and during early conception attempts. With proper treatment and follow up, many people with hyperthyroidism go on to conceive successfully.

Next steps: Getting your thyroid tested and treated

Most cases of hypothyroidism can be treated with oral medication after consulting with your doctor. There are also several treatment options for hyperthyroidism, depending on the cause.

If you’re experiencing symptoms, feeling “off,” or you simply want to check your thyroid before TTC, testing can give you clarity and a plan.

Labcorp OnDemand’s Thyroid Stimulating Hormone Blood Test measures TSH, a hormone that stimulates the thyroid to produce T3 and T4, two hormones that play a critical role in controlling the body’s metabolism. After easily purchasing it with a credit card or using your HSA/FSA, you can visit a convenient Labcorp patient service center for blood collection. Results are delivered to you in just a couple of days. Click here to learn more!