Hypothyroidism (underactive thyroid)

Hypothyroidism (underactive thyroid) means that the thyroid gland doesn’t create and release the amount of thyroid hormones that your body needs. Your thyroid is an organ at the bottom front of your neck in the shape of a butterfly. Without enough thyroid hormones, your metabolism slows down; the menstrual cycle and fertility are affected too. Hypothyroidism is a common condition among women who struggle to get pregnant. 2-4% of women in the reproductive age group have hypothyroidism.

This article has been verified by a medical professional

Impact on fertility

The thyroid hormones affect several other important reproductive hormones, including FSH, LH, estrogen, androgens, progesterone, and prolactin. Hypothyroidism causes anovulation (meaning that no egg gets released by the ovaries). It can also interfere with the luteal phase, which makes it more difficult for an egg to implant in the womb – this can cause IVF to fail. For women who are able to conceive, untreated hypothyroidism can lead to miscarriage, high blood pressure, gestational diabetes, placental abruption (when the placenta detaches from the inner wall of the uterus), premature birth, stillbirth, and low birth weight.

Diagnosis

Healthcare providers diagnose hypothyroidism based on a blood test. Slightly elevated TSH levels with normal levels of thyroid hormones T3 and T4 indicate subclinical hypothyroidism. High levels of TSH and low levels of T3 and T4 indicate clinical hypothyroidism.

Potential causes

The most common cause of hypothyroidism is a hereditary autoimmune disorder called Hashimoto’s thyroiditis, which causes the immune system to damage the thyroid gland.

Other causes of hypothyroidism include:

• Inflammation of the thyroid gland
• Iodine deficiency (a mineral your thyroid needs to produce hormones)
• Genetic health conditions
• Surgical removal of the thyroid gland
• Viral illnesses
• Pregnancy (postpartum thyroiditis)

Additionally, hypothyroidism is associated with elevated levels of the hormone prolactin, a condition called hyperprolactinemia, which also reduces fertility. Around 46% of women struggling to get pregnant who have hypothyroidism have hyperprolactinemia as well.

Symptoms

Hypothyroidism has the following physical signs:

• Heavy and frequent periods
• Fatigue
• Sore or cramped muscles
• Poor memory
• Dry skin and hair
• Weight gain
• Cold sensitivity
• Loss of sex drive
• Constipation

Treatment to improve fertility

Thankfully, hypothyroidism is something that can be easily managed with medication that increases your thyroid hormone levels. A commonly prescribed medication is L-thyroxine. This normalizes the menstrual cycle along with prolactin levels and boosts fertility.

As soon as your thyroid hormones are back in balance, you should be able to get pregnant and have a healthy pregnancy. A study found that over 76% of women with hypothyroidism who couldn’t conceive were able to get pregnant between 6 weeks to 1 year after starting medication.

Certain dietary changes can also help keep your thyroid healthy. Check vitamin D, iron, and zinc levels, and talk to your doctor about supplementation if necessary, as these are all important for the thyroid. In addition, increasing your intake of iodine-rich foods such as seafood can help with hypothyroidism.

Once you get pregnant, be sure to tell your OB-GYN that you have an underactive thyroid. Your medication dosage will likely need to be adjusted and you’ll need to be more closely monitored during your pregnancy.

This article has been verified by a medical professional

• Pregnancy and fertility in thyroid disorders. British Thyroid Foundation. Accessed 01 July 2022.
• Hypothyroidism and infertility: Any connection? Mayo Clinic. Accessed 01 July 2022.
• Verma I et al.: Prevalence of hypothyroidism in infertile women and evaluation of response of treatment for hypothyroidism on infertility. Int J Appl Basic Med Res. 2012;2(1):17-19.
• Unuane D, MD, PhD & Velkeniers B, MD, PhD: Impact of thyroid disease on fertility and assisted conception. Best Practice & Research Clinical Endocrinology & Metabolism. 2020;34(4):101378.
• P. Monteleone et al.: Female infertility related to thyroid autoimmunity: the ovarian follicle hypothesis. Am J Reprod Immunol. 2012;66:108-114.
• The Connection Between Thyroid Disorders and Fertility. EndocrineWeb. Accessed 01 July 2022.
• Gude D: Thyroid and its indispensability in fertility. J Hum Reprod Sci. 2011;4(1):59-60. 
• General Information/Press Room. American Thyroid Association. Accessed 06 July 2022.
• Hyperthyroidism (overactive thyroid). Mayo Clinic. Accessed 06 July 2022.
• Underactive thyroid (hypothyroidism) Symptoms. NHS. Accessed 06 July 2022.
• Rugge JB et al: Screening for and Treatment of Thyroid Dysfunction: An Evidence Review for the U.S. Preventive Services Task Force. Agency for Healthcare Research and Quality (US). 2014. Rockville (MD).
• Shrestha S et al.: Association of Thyroid Profile and Prolactin Level in Patient with Secondary Amenorrhea. Malays J Med Sci. 2016;23(5): 51-56.
• Hyperthyroidism and Graves’ Disease. University of Michigan Health. Accessed 02 September 2022.
• Thyroid – hyperthyroidism. Better Health, from the Department of Health, State Government of Victoria, Australia. Accessed 02 September 2022.
• Hypothyroidism. Cleveland Clinic. Accessed 07 September 2022.  
• Hypothyroidism in Pregnancy: Causes, Complications and Treatment. Pace Hospitals. Accessed 07 September 2022.