Thyroid Health, Toxic Metals & Fertility Before Pregnancy

Preparing for a healthy pregnancy starts before conception. Thyroid function, nutritional status, and environmental exposures can all influence reproductive health and the developing baby. Although many people focus on fertility once they begin trying to conceive, the months leading up to pregnancy provide an important opportunity to identify potential health concerns and reduce avoidable risks.

Among the factors worth considering are thyroid hormone balance and exposure to toxic metals- including mercury, cadmium, arsenic, and lead. Understanding how these factors interact can help individuals make informed decisions about preconception testing, nutrition, and environmental health.

Why Thyroid Health Matters BEFORE Pregnancy

The thyroid gland produces hormones that regulate metabolism, energy production, body temperature, and numerous other physiological processes. Thyroid hormones also play an essential role in reproductive function and early fetal development.

The two primary thyroid hormones are thyroxine (T4) and triiodothyronine (T3). T4 serves largely as a circulating precursor that can be converted into the more biologically active T3 in tissues throughout the body.

Thyroid function is regulated by thyroid-stimulating hormone (TSH), which is produced by the pituitary gland. Thyroid hormone production also depends on adequate iodine intake, while selenium, iron, and other nutrients contribute to normal thyroid function.

Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can affect reproductive health. Thyroid disorders may be present even when symptoms are subtle or attributed to stress, lifestyle, or other health concerns.

Thyroid Hormones and Female Fertility

Thyroid hormones influence several processes involved in conception, including menstrual cycle regulation, ovulation, and interactions between the brain, pituitary gland, and ovaries.

Overt hypothyroidism has been associated with menstrual irregularities, ovulatory dysfunction, and difficulties conceiving. It can also increase the risk of adverse pregnancy outcomes if inadequately treated. Hyperthyroidism may similarly interfere with menstrual function and pregnancy health.

Thyroid dysfunction can also influence prolactin levels. In some people with hypothyroidism, elevated prolactin may disrupt normal reproductive hormone signalling and ovulation.

Autoimmune thyroid disease, including Hashimoto thyroiditis, deserves consideration during preconception care. Thyroid antibodies can be present even when TSH and thyroid hormone levels are within their reference ranges.  The presence of thyroid or other autoimmune antibodies may indicate testing for other autoimmune conditions such as celiac disease, which- if untreated, can also contribute to poor fertility outcomes.

Importantly, not every person experiencing infertility has a thyroid disorder, and treating people with normal thyroid function does not necessarily improve fertility. Thyroid assessment should be guided by medical history, symptoms, risk factors, and appropriate clinical guidelines.

Thyroid Hormones and Male Fertility

Thyroid hormones also influence male reproductive health. Abnormal thyroid function has been associated with changes in sperm concentration, motility, morphology, and sexual function.

Because sperm development takes approximately 3 months, addressing relevant health concerns before conception may be beneficial. A preconception approach that considers both partners can help identify potentially modifiable factors rather than focusing exclusively on female reproductive health.

Thyroid Hormone and Fetal Development

Thyroid health becomes particularly important during early pregnancy.

During the first trimester, the developing fetus depends heavily on maternal thyroid hormone, especially T4, because the fetal thyroid gland is not yet fully functional. The fetal thyroid begins developing early in pregnancy, but its ability to produce sufficient hormone matures later.

Maternal thyroid hormone supports the formation and development of the fetal brain and nervous system. It contributes to neuronal migration, differentiation, myelination, and other processes involved in neurological development.

Severe maternal iodine deficiency and inadequately treated overt hypothyroidism are established concerns because they can compromise pregnancy outcomes and fetal development. Maternal thyroid dysfunction has also been associated with miscarriage, preterm birth, and other complications.

The relationship between mild or subclinical thyroid abnormalities and child neurodevelopment is more complex. Studies have not consistently demonstrated that treating every mild laboratory abnormality improves developmental outcomes. This is why thyroid results should be interpreted in the context of pregnancy status, laboratory-specific reference ranges, thyroid antibodies when indicated, and individual risk factors.

Identifying and appropriately managing thyroid disease before conception can reduce avoidable risks and support a healthier pregnancy.

Preconception Care: More Than Fertility Testing

Preconception care is an opportunity to assess health before pregnancy begins- ideally several months before trying to conceive.

Rather than focusing only on reproductive hormones, a comprehensive assessment can consider thyroid and other endocrine function, nutritional status, blood sugar regulation, medication and supplement use, chronic health conditions, and relevant environmental exposures.

Depending on the individual’s history and risk factors, preconception care may include:

• Reviewing thyroid symptoms, personal and family history, previous thyroid results and personal or family history of autoimmune conditions
• Assessing TSH and free T4 when clinically indicated, with thyroid antibodies considered in appropriate circumstances
• Reviewing iodine intake and ensuring adequate—but not excessive—iodine consumption
• Assessing iron status and other nutrients when indicated
• Reviewing medications, supplements, occupational exposures, hobbies, and potential sources of environmental contaminants
• Discussing nutrient supplementation, alcohol and tobacco avoidance, and other established preconception recommendations
• Evaluating the menstrual cycle, ovulation, and relevant reproductive health concerns
• Discussing semen analysis and relevant medical assessment for the male partner when indicated

The goal is not to test everyone for everything. Testing should be individualized according to clinical history, symptoms, exposure risk, and whether the result would change management.

Toxic Metals and Reproductive Health

Environmental toxic metals can enter the body through food, drinking water, air, dust, occupational activities, and certain consumer products. Some metals can persist in the body or accumulate in particular tissues, while others are cleared more readily.

Mercury, cadmium, arsenic, and lead are of particular concern because exposure can affect multiple organ systems. Research has also investigated their potential effects on reproductive hormones, egg and sperm quality, pregnancy outcomes, and fetal development.

1. Mercury: A concern for the developing nervous system

Mercury exposure occurs in several forms. Methylmercury is primarily associated with certain fish and seafood, while elemental mercury and inorganic mercury compounds have different exposure sources and toxicological properties.

Methylmercury can cross the placenta and reach the developing fetal brain. Prenatal exposure at sufficiently high levels can harm neurological development, which is why reducing avoidable exposure during preconception and pregnancy is important.

Research has also examined mercury’s potential effects on reproductive hormones, sperm quality, and fertility. However, findings vary, and the evidence for direct effects on human fertility at typical environmental exposure levels is less conclusive than the evidence for developmental neurotoxicity.

Practical steps: choose fish lower in mercury and limit your fish intake to once per week or less and consider occupational or other exposure sources when relevant.  Skin lightening creams and topical treatments acquired outside of North America often use mercury as a key ingredient.  Talk to your clinician about testing for mercury and re-test after intervention.

2. Cadmium: Potential effects on the ovaries, testes, and placenta

Cadmium is a toxic metal found in tobacco smoke, certain occupational environments, contaminated soil, and some foods. Because the body eliminates cadmium slowly, repeated exposure can contribute to accumulation over time.

Experimental studies suggest that cadmium can interfere with oxidative balance, cellular signalling, and hormone-related processes. Research has also explored its effects on ovarian function, sperm quality, implantation, and placental function.

Human studies have reported associations between cadmium exposure and certain reproductive outcomes, but results are not uniform. Exposure measurement, smoking, nutrition, and other environmental factors can complicate interpretation.

Cadmium is also a kidney toxicant and can affect bone health. Reducing tobacco smoke exposure and addressing identifiable occupational or environmental sources are reasonable preventive measures.

Practical steps: avoid smoking and secondhand smoke where possible, use appropriate workplace protections, and investigate known environmental contamination when there is a credible reason to suspect exposure.  Discuss heavy metals testing with your clinician.

3. Arsenic: Drinking water and early development

Arsenic occurs naturally in some groundwater and can also enter the environment through industrial and agricultural activities. Inorganic arsenic is the form of greatest concern for many environmental exposure scenarios.

Long-term exposure to inorganic arsenic is associated with several adverse health effects, including certain cancers and cardiovascular disease. Prenatal and early-life exposure has also been investigated in relation to fetal growth, birth outcomes, and childhood neurodevelopment.

Arsenic exposure may affect cellular signalling, oxidative stress, and processes involved in normal development. Some studies have examined associations with pregnancy complications and reproductive outcomes, although the evidence varies by exposure level and population.

Because arsenic can occur in drinking water and some foods, identifying the actual source is important. Rice and rice-based products can contribute to dietary exposure, particularly when they make up a large proportion of the diet.

Practical steps: if drinking water comes from a private well or there is a known contamination concern, use appropriate accredited testing and filtration of any water meant to be ingested (i.e. for drinking or food preparation). Vary grain choices rather than relying heavily on rice-based products, particularly for young children.  Consider gluten-free grains such as buckwheat, teff and sorghum.

4. Lead: A preventable risk before and during pregnancy

Lead is a well-established developmental toxicant. Exposure may occur through deteriorating lead-based paint in older buildings, contaminated dust or soil, some plumbing systems, certain occupational activities, and particular imported products (i.e. toys, candy, unregulated herbal medicines).

Lead can remain in the body for years and may be stored in bone. During pregnancy, changes in bone metabolism can mobilize some stored lead into the bloodstream, creating a potential source of fetal exposure even if the original exposure occurred long before conception.

Lead exposure has been associated with adverse reproductive outcomes, including reduced fertility in some populations, pregnancy complications, and impaired fetal growth. Prenatal exposure can also affect the developing nervous system. No safe blood lead level has been identified for children, and prevention is especially important before pregnancy.  

Practical steps: assess potential exposure from older housing, renovation dust, drinking water, workplace activities, and relevant hobbies. If exposure is suspected, a clinician can determine appropriate testing and intervention.

How Might Toxic Metals Affect Thyroid Function?

The thyroid gland depends on tightly regulated hormone production, conversion, transport, and signalling. Some toxic metals have been investigated for their potential to interfere with these processes.

Laboratory and animal studies suggest that certain metals may affect oxidative stress, thyroid enzyme activity, hormone metabolism, or the hypothalamic-pituitary-thyroid axis. Human studies have explored associations between metal exposure and changes in TSH, T4, T3, or thyroid antibodies.

Effects of toxic metals may differ according to the chemical form of the metal, dose, duration of exposure, nutritional status, ability to detoxify, and the presence of other environmental contaminants.

It is therefore premature to conclude that a particular toxic metal is the cause of an individual’s thyroid symptoms or abnormal thyroid results without appropriate clinical assessment and exposure evidence.

Where there is a credible history of exposure, evaluating both thyroid health and the exposure itself may be reasonable. The focus should be on identifying the source, measuring exposure with validated methods, and reducing further contact—not assuming that every nonspecific symptom reflects heavy metal toxicity.

Supporting Thyroid Health and Reducing Exposure Before Conception

Preconception care should prioritize evidence-based measures that support reproductive health while avoiding unnecessary testing and treatment.

1. Identify and manage thyroid dysfunction

Discuss thyroid assessment with a qualified healthcare professional if there are relevant symptoms, a history of thyroid disease, irregular menstrual cycles, infertility, autoimmune disease, or other clinical risk factors.

TSH is commonly used as an initial test, with free T4 and additional investigations selected according to the findings. People taking thyroid medication should review their treatment plan before conception because thyroid hormone requirements can change early in pregnancy.

Do not start or adjust thyroid medication or high-dose iodine supplements without medical guidance.

2. Optimize nutrition without over-supplementing

Adequate iodine is necessary for thyroid hormone production, but excessive iodine can also disrupt thyroid function. Selenium is important for thyroid hormone metabolism, but supplementation beyond nutritional needs is not automatically beneficial.

Iron deficiency should be identified and managed when present. Adequate folate, protein, and other essential nutrients also support preconception health.

A prenatal supplement containing an appropriate amount of folate is recommended for most people planning pregnancy, with dose and formulation individualized according to medical history and applicable guidelines.

3. Reduce avoidable environmental exposures

Review potential exposure sources at home, work, and through diet. Practical steps may include testing private well water when appropriate, reducing tobacco smoke exposure, following fish-consumption guidance, and using proper protection during renovation or occupational activities.  Effective air and water filtration can help with reducing the ingestion of toxic metals as well as other environmental toxins.  Ensure that your personal care products and supplements have been tested for contamination.

4. Use validated testing when exposure is suspected

Speak with your clinician regarding validated methods of testing for toxic metals. In most cases such methods include urine testing and blood testing.

5. Avoid unsupervised chelation and aggressive detoxification

Chelation is a medical treatment used for selected cases of confirmed metal poisoning. It is not a routine preconception wellness intervention and should not be used simply because a test detects a metal.

Chelating agents can cause adverse effects, including depletion of essential minerals, kidney injury, and other complications. There is also insufficient evidence that aggressive detoxification protocols improve fertility or fetal outcomes in people without established poisoning.

When a significant exposure is identified, treatment should be directed by a clinician experienced in medical toxicology or environmental medicine, with pregnancy planning considered in the management strategy.

Healthy thyroid function and thoughtful preconception care are important components of preparing for pregnancy. Thyroid hormones support ovulation, reproductive function, and early fetal brain development. At the same time, exposure to toxic metals- including mercury, cadmium, arsenic, and lead, can pose health risks, particularly during sensitive periods of fetal development.

The most useful approach is proactive and evidence-informed: identify and manage thyroid disorders, ensure adequate nutrition, review environmental exposure risks, and use targeted testing when clinically justified.

A personalized preconception plan can help distinguish established risks from uncertain associations and prioritize interventions that are safe, appropriate, and supported by evidence.

References

1. Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid. 2017;27(3):315-389. doi:10.1089/thy.2016.0457. Read article
2. Korevaar TIM, Medici M, Visser TJ, Peeters RP. Thyroid disease in pregnancy: new insights in diagnosis and clinical management. Nat Rev Endocrinol. 2017;13(10):610-622. doi:10.1038/nrendo.2017.93.
3. Moog NK, Entringer S, Heim C, Wadhwa PD, Kathmann N, Buss C. Influence of maternal thyroid hormones during gestation on fetal brain development. Neuroscience. 2017;342:68-100. doi:10.1016/j.neuroscience.2015.09.070.
4. Practice Committee of the American Society for Reproductive Medicine. Subclinical hypothyroidism in the infertile female population: a guideline. Fertil Steril. 2024;121(5):765-782. doi:10.1016/j.fertnstert.2023.12.038.
5. World Health Organization. Guideline: Optimal Serum and Red Blood Cell Folate Concentrations in Women of Reproductive Age for Prevention of Neural Tube Defects. World Health Organization; 2015.
6. US Centers for Disease Control and Prevention. About lead and other heavy metals and reproductive health. Updated February 14, 2024. Accessed October 10, 2026. CDC resource.
7. US Centers for Disease Control and Prevention. Risk factors and pregnancy: lead exposure. Updated August 25, 2026. Accessed October 10, 2026. CDC resource.
8. World Health Organization. Arsenic. Published December 7, 2022. Accessed October 10, 2026. WHO fact sheet.
9. Vahter M. Effects of arsenic on maternal and fetal health. Annu Rev Nutr. 2009;29:381-399. doi:10.1146/annurev-nutr-080508-141102.
10. Eum KD, Lee MS, Paek D. Cadmium in blood and hypertension. Sci Total Environ. 2008;387(1-3):78-85. doi:10.1016/j.scitotenv.2007.07.045.
11. Taylor CM, Golding J, Emond AM. Blood mercury levels and fish consumption in pregnancy: risks and benefits for birth outcomes in the ALSPAC birth cohort. Int J Hyg Environ Health. 2016;219(3):253-260. doi:10.1016/j.ijheh.2016.01.002.
12. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Lead. US Department of Health and Human Services; 2020.
13. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Mercury. US Department of Health and Human Services; 2024.
14. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Cadmium. US Department of Health and Human Services; 2012.
15. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Arsenic. US Department of Health and Human Services; 2007.
16. Heavy metals and human reproductive toxicity: mechanisms, pregnancy outcomes, and mitigation strategies. Reprod Toxicol. 2026;139:109104. doi:10.1016/j.reprotox.2025.109104.