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

Fertility isn’t separate from the rest of the body. Your reproductive system is part of the endocrine system, which means it runs on hormones. Your ovaries aren’t just releasing eggs each month, they’re hormone-producing powerhouses, sending estrogen and progesterone into the bloodstream and constantly communicating with your brain and the rest of your body.

The thyroid is part of that same hormone network. When it’s out of sync, it can throw off more than just your energy levels; it can affect ovulation, cycles, and fertility too. Let’s break down how it all connects.

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

The thyroid is a small, butterfly-shaped gland at the base of your neck, but don’t let its size fool you. It plays a major role in the endocrine system, helping regulate metabolism, body temperature, heart rate, digestion, and more. That’s why thyroid issues can show up in ways that feel totally unrelated at first.

Here’s the quick science: your pituitary gland releases TSH (thyroid-stimulating hormone), which tells your thyroid how much T3 and T4 to make. Those hormones don’t just manage energy, they also interact with your reproductive hormones. When thyroid levels are too high or too low, ovulation and cycle regularity can get thrown off. A 2021 study published in Thyroid Research found thyroid hormones directly influence ovarian function, including follicle development and ovulation. And a 2020 review in Best Practice & Research Clinical Endocrinology & Metabolism linked even mild or subclinical thyroid dysfunction with ovulatory disorders and reduced fertility.

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 act directly on the ovaries and uterine lining. A 2020 study published in JBRA Assisted Reproduction found thyroid hormone receptors in both ovarian tissue and the endometrium, pointing to a direct role in egg maturation and implantation.

Thyroid health also matters after you conceive. In early pregnancy, your baby relies entirely on your T4 supply. A 2024 review in Cureus found untreated thyroid disorders are associated with higher risks of miscarriage and implantation failure, which is why thyroid testing is often part of fertility workups.

The hopeful part? Thyroid-related fertility challenges are often very treatable. Once levels are properly managed, many people see improvements in ovulation, cycle regularity, and pregnancy outcomes.

TSH level to get pregnant: What's ideal?

If you’re TTC, many reproductive endocrinologists aim for a TSH under 2.5 mIU/L. That’s lower than the standard “normal” lab range (which often goes up to 4.0 or 4.5) but pregnancy puts extra pressure on your thyroid.

According to the American Endocrine Society, people trying to conceive or in early pregnancy are often advised to keep TSH below 2.5 mIU/L, especially in the first trimester when the embryo relies entirely on your thyroid hormone.

Research backs this up. A 2023 study in Human Reproduction Open found that women with subclinical hypothyroidism had higher miscarriage rates and lower live birth rates compared to those with TSH under 2.5 mIU/L. And a 2015 Cochrane Library review found that identifying and treating thyroid dysfunction before pregnancy was associated with improved fertility and pregnancy outcomes.

That’s why checking TSH before TTC can be empowering. It gives you time to optimize levels proactively. If you’re adjusting medication or newly pregnant, most providers recheck TSH every 4 to 6 weeks, since levels can shift quickly.

Getting pregnant with hypothyroidism

When your thyroid doesn’t make enough hormone, it’s called hypothyroidism. It can slow everything down (your metabolism, your energy, even your digestion) leading to symptoms like fatigue, weight gain, constipation, and feeling cold all the time.

It can also affect your cycle. Hypothyroidism is linked to irregular periods and missed ovulation. A 2015 review in Clinical and Experimental Reproductive Medicine found thyroid dysfunction is associated with ovulatory disorders that can make conception harder.

Hypothyroidism can also affect progesterone in the second half of your cycle. Since progesterone helps support implantation and early pregnancy, lower levels may make it harder for an embryo to stick.

Untreated hypothyroidism is also linked to a higher risk of miscarriage. A 2013 study published in The Journal of Obstetrics and Gynecology of India found that both overt and subclinical hypothyroidism were associated with increased pregnancy loss, especially when TSH was elevated early in pregnancy.

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

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. With both, ovulation may be inconsistent, delayed, or not happen at all without treatment.

Thyroid and implantation failure

Thyroid antibodies don’t just affect hormone levels, they may also impact implantation. A 2023 review in the International Journal of Molecular Sciences found that autoimmune thyroid disease is linked to changes in immune signaling that can interfere with implantation and early placental development.

Dr. Buckheit keeps it grounded: “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.”

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.

Does hyperthyroidism affect fertility?

Yes, it can. Hyperthyroidism happens when your thyroid is overactive and produces too much T4. That can rev up your metabolism and cause symptoms like weight loss, anxiety, sleep disruption, and lighter or irregular periods.

You can get pregnant with hyperthyroidism, but untreated levels can make it harder. The British Thyroid Foundation notes that uncontrolled hyperthyroidism is linked to menstrual irregularities, ovulatory dysfunction, and reduced fertility. A 2022 review from the American Thyroid Association also found that thyroid hormone imbalance can negatively affect ovarian function and follicle development, which can mean missed or unpredictable ovulation.

When hyperthyroidism isn’t managed, it’s associated with higher risks of miscarriage, preterm birth, and other pregnancy complications. The good news? Getting thyroid levels under control before and during pregnancy significantly lowers those risks.

Graves’ disease and fertility

Graves’ disease is an autoimmune condition and the most common cause of hyperthyroidism. It can affect fertility in two ways: through elevated thyroid hormone levels and through underlying autoimmune activity

Treatment often includes antithyroid medication, and in some cases more definitive treatment before pregnancy. The right approach depends on your timeline and how well your condition is controlled. Providers usually monitor both thyroid hormone and antibody levels before and during pregnancy to help reduce risks and support a healthy outcome.

How to lower TSH levels to get pregnant (and when you actually need to)

If your TSH is high because of hypothyroidism, levothyroxine is the standard treatment. It replaces the thyroid hormone your body isn’t making enough of and helps bring TSH down. When properly monitored, it’s considered safe and effective for people who are TTC and during pregnancy. But try not to self medicate, megadose iodine, or rely on detoxes or supplements to “fix” TSH. These approaches can backfire.

After starting or adjusting medication, providers usually recheck TSH in about 4 to 6 weeks. It can take some time to reach a fertility supportive range, which is why testing before TTC can make a big difference.

Sleep, stress support, and correcting nutrient deficiencies can help overall thyroid health, but if true hypothyroidism is present, medication is the primary and most reliable tool.

How to lower thyroid levels to get pregnant

If your T3 and T4 levels are too high, that means hyperthyroidism. The goal is to bring thyroid hormone back into range so ovulation and early pregnancy can happen safely.

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

First line treatment is usually medication. Methimazole and propylthiouracil (PTU) lower thyroid hormone production, and your provider will choose based on your situation and timing. Radioactive iodine is not safe if you are TTC or pregnant, and pregnancy is typically delayed for at least six months after treatment. In some cases, surgery is considered.

Just as with TSH, levels are usually monitored every 4 to 6 weeks while adjusting treatment. With the right care and follow up, many people with hyperthyroidism go on to conceive successfully.

Next steps: Getting your thyroid tested and treated

If your thyroid is underactive, treatment is often straightforward. Most cases of hypothyroidism are managed with daily oral medication prescribed by your provider. Hyperthyroidism has several treatment options too, depending on the cause and your pregnancy timeline.

If you have symptoms, feel “off,” or just want peace of mind before TTC, asking for thyroid testing can give you clarity and a concrete plan. You deserve answers and support, especially when it comes to your fertility.