How do thyroid hormone levels impact fertility?

Thyroid disorders (hypothyroidism and hyperthyroidism) can negatively impact fertility by affecting both the ability to become pregnant and the ability to carry a baby to term. In addition, the presence of autoimmune antibodies with or without hypothyroidism and hyperthyroidism can impact your fertility.

Thyroid disorders impair fertility by preventing ovulation and possibly even embryo implantation. If left untreated during pregnancy, it can cause miscarriage, premature birth and low birthweight. If you have been diagnosed with a thyroid disorder, it is important to check blood levels regularly according to your doctor’s recommendation to make sure your medication dosage is appropriate, and to adjust the dosage as needed.

The thyroid produces two hormones, triiodothyronine (T3) and thyroxine (T4). Overproduction (hyperthyroidism) and underproduction (hypothyroidism) are conditions where too much or too little of these thyroid hormones are produced. If uncontrolled, both of these have been linked to issues with fertility, pregnancy complications and fetal health issues.

When the thyroid is dysregulated, it can cause a number of issues including:

• Changes in the menstrual cycle
• Disruption to egg release from the ovaries (ovulation)
• Development of ovarian cysts
• Increased risk of miscarriage
• Increased risk of premature birth
• Increased risk of preeclampsia

Thyroid antibodies can affect the immune system. This can lead to difficulty with egg fertilization or implantation, and it can increase the risk of miscarriage.

Thyroid issues can also affect males, although women are usually affected more frequently. Thyroid dysregulation in men can potentially affect sperm quality and motility. Checking thyroid level in men, however, is not part of standard of care, unless there is a reason to suspect a thyroid issue.

How are thyroid issues identified and treated?

Identifying thyroid issues is important for female patients that are looking to get pregnant. Early diagnosis means early intervention, which increases the chances of conception. This is especially important if you already have known thyroid issues.

Thyroid dysregulation can be identified by testing the blood levels of thyroid-stimulating hormone (TSH). Elevated TSH means the thyroid hormone is not making enough thyroid hormone, indicating hypothyroidism. Conversely, when TSH is too low and thyroid hormone levels are high, it could be due to hyperthyroidism.

Doctors may also measure levels of free T4 and Total T3, and the thyroid antibodies levels since sometimes the body can make antibodies against your thyroid. Regular thyroid levels should be taken if you have a thyroid disorder and are trying to get pregnant.

Treatment varies depending on a diagnosis of hypothyroidism or hyperthyroidism. Doctors will recommend frequent follow up of the hormone levels to determine if changes in therapy are needed.

Dietary changes can also improve thyroid levels. In particular, iodine and selenium can benefit individuals who have thyroid issues. Iodine is a component of thyroid hormones, so lack of this micronutrient can lead to insufficient T3 and T4 production. Vitamin D has been shown to lower thyroid antibodies, which in turn may contribute to improved fertility.

How do thyroid levels change during pregnancy?

Thyroid levels vary throughout pregnancy. During pregnancy, human chorionic gonadotropin (hCG) and estrogen production cause natural changes in thyroid hormone. Produced by the placenta, hCG stimulates the thyroid to produce more thyroid hormones. Estrogen increases thyroid-binding globulin that enables the body to transport more thyroid through the blood.

There are specific guidelines for target TSH levels in pregnancy depending on which trimester you are in.

• First trimester — 0.1-2.5 uIU/ml
• Second trimester — 0.2-3.0 uIU/ml
• Third trimester — 0.3-3.0 uIU/ml

Ideal levels are TSH levels between 0.5-2.5 uIU/ml. Thyroid hormones are essential to the development of the baby during pregnancy. At around 12 weeks of gestation, the baby will start to produce its own thyroid hormones.

If you are pregnant, it’s important that your thyroid levels are monitored and normalized. While thyroid conditions can impact fertility, pregnancy is possible by properly regulating your thyroid levels.

After pregnancy, blood levels should be measured once again to check and any necessary changes should be made to medication dose. Usually, it returns to the pre-pregnancy dosage.

Key Takeaway

If you have concerns about your thyroid levels, or have a family history of thyroid disorder, and want to get pregnant, it is worth getting your hormone levels checked, so that any necessary treatment can be initiated. Balancing your thyroid hormone levels through medications and lifestyle interventions will greatly increase your fertility and your chances of conception.

If you are planning on starting or growing your family, check out our expert guides on all things genetics and fertility. Today, advanced genetic screening is now available to couples who want their child to have the best shot of a healthy life. Explore how Orchid helps you conceive with confidence.