How Thyroid Function Can Affect Fertility

Saturday, October 5, 2019
How Thyroid Function Can Affect Fertility

As someone who has struggled with both infertility and hyperthyroidism (specifically an autoimmune condition called Grave’s disease), I feel the need to remind everyone and emphasize how important thyroid health is to our fertility. 

Hyperthyroidism (an overactive thyroid gland) can lead to very light or irregular periods, infertility, miscarriage, as well sa preterm labor. 

The typical symptoms of hyperthyroidism include:

a fast heart rate (tachycardia) of more than 90 beats per minute 

irregular heartbeat (cardiac arrhythmia - often in the form of PVCs and sometimes atrial fibrillations)

anxiety and panic attacks

insomnia and restless sleep

unexplained weight loss

Hyperthyroidism is usually treated either with antithyroid medication (methimazole or PTU - propylthiouracil), radioactive iodine or surgery. None of these options are considered particularly safe to use during pregnancy, but PTU is the preferred medication during the first trimester, since it has the lowest risk of causing birth defects in the baby. Often, hyperthyroidism symptoms tend to worsen during the first trimester, due to the HCG pregnancy hormone that stimulates the thyroid gland. During the second and third trimester, the immune suppression created by the advancing pregnancy tends to relieve hyperthyroidism of autoimmune origin (like Grave’s).

Ideally, when discovered on time, hyperthyroidism can be treated and will go into remission before becoming pregnant. In Grave’s disease however, TSH receptor auto-antibodies (TRAb) circulating in the maternal blood might still affect the pregnancy, even when the thyroid hormone levels are normal, so close monitoring is important.

Hypothyroidism (an underactive thyroid) can cause heavy, prolonged periods, as well as absent periods, anovulation, anemia, inability to get pregnant and miscarriage. 

Its usual symptoms are:

fatigue and an increased need for sleep

unexplained weight gain

brain fog, poor memory and inability to focus


thinning hair

slow heart rate (bradycardia) of less than 60 beats per minute

Hypothyroidism can be easily treated with a daily dose of synthetic thyroid hormone (levothyroxine), which is safe to take throughout pregnancy as well. The dosage needs to be periodically reassessed and re-adjusted to keep your thyroid levels in a healthy range. In Hashimoto’s hypothyroidism, which is an autoimmune condition just like Grave’s, the circulating auto-antibodies (anti-TPO and anti-TG) may remain high and possibly affect the pregnancy even when the thyroid hormone levels are back to normal, so extra care needs to be taken by your doctor.

If you are trying to conceive (and even if you’re not), it’s a very good idea to check your thyroid hormone levels. A thyroid panel that measures your TSH, FT4 and FT3 hormones will help your doctor discover if you have a thyroid disorder that may affect your overall health and fertility as well. Thyroid conditions are extremely common in young reproductive-age women and up to 60% of them are unaware they even have one.

More than that, keep in mind that the TSH level for a woman who is trying to get pregnant should be somewhere between 0.5 and 2.0 which is the best range for optimum fertility. Anything over 2.5 (despite still being considered in the ‘normal’ range) can lower the chances of pregnancy and increase the odds of being diagnosed with unexplained infertility. If your TSH level is higher than 2.5, your should definitely discuss this with a Reproductive Endocrinologist (RE) since it can easily be fixed.