In this article:
- What is hypothyroidism?
- How does hypothyroidism affect fertility?
- What is the impact of birth control pills?
- How do you reduce your risk?
What is hypothyroidism?
The thyroid is the butterfly-shaped gland at the base of your neck. As part of the endocrine system, it makes and stores hormones that help regulate your body's energy use, along with many other essential functions.
Hypothyroidism is caused by an underactive thyroid gland. When your thyroid hormone production drops, your body processes slow down and change. Hypothyroidism can affect many different systems in your body, including the menstrual cycle.
How does hypothyroidism affect fertility?
Ovulation is the monthly process in which the female reproductive system produces an egg. During ovulation, the pituitary gland, often called the "master gland," releases follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH acts as a 'messenger' to stimulate the development of follicles in the ovaries, and LH helps to regulate the menstrual cycle and egg production.
Luteinizing hormone and follicle-stimulating hormone levels rise and fall together during the monthly cycle. The amount of LH present in a women's body depends on the phase of her menstrual cycle. When LH peaks, it signals to the ovaries to release an egg.
You are most fertile the day an egg is released from the ovary, and a few days beforehand. Having sex during this window gives you the best chance of getting pregnant.
However, the Kobe University School of Medicine in Japan suggests that one of the factors responsible for successful induction of ovulation is an adequate circulating level of thyroid hormones, and a study in the Journal of Applied and Basic Medical Research found that a shocking 2-4% of women in the reproductive age group have low thyroid hormone levels.
Many of our hormones are part of a regulatory hormonal cascade, so when thyroid hormone production drops, LH levels may also remain low. Therefore, one possible symptom of hypothyroidism is that ovulation may not occur or may not happen with any regularity.
This thyroid dysfunction may result in irregular menstrual cycle patterns, abnormal endometrial development, high prolactin levels, or sex hormone imbalances. All of these can affect fertility.
What is the impact of birth control pills?
Birth control is a way for men and women to prevent pregnancy, and it comes in many different forms, including hormonal contraception like "the pill."
"The pill" contains synthetic estrogen and progestin hormones that work to inhibit the body's natural hormone cycles. It usually stops the body from ovulating and can also change the cervical mucus making it hard for the sperm to find an egg.
Estrogen causes an increase in thyroxine-binding globulin (TBG) levels. TBG is a protein that helps to move thyroid hormones throughout your body. This rise in TBG means there is less free thyroid hormone available, which affects how much thyroid replacement hormone you need.
Several studies indicate that hormonal birth control interferes with the absorption of some of the nutrients that your thyroid needs to make the thyroid hormone, thyroxine (T4), such as selenium, zinc, and magnesium. Without proper absorption, the body does not receive appropriate amounts of these nutrients, and the thyroid cannot function optimally.
While these micronutrients are in many common foods, it's widely known that there is a difference in bioavailability between food intake and supplementation. Factors like cooking, storage, and processing can affect the amount of vitamins and minerals available in food form.
Many of the side effects of hormonal birth control are reversible.
How do you reduce your risk?
Of course, normal thyroid function is necessary for fertility and a healthy pregnancy.
Test Your Thyroid
Work with your care team to understand how your thyroid is functioning and if there may be a need for further evaluation. While many labs only look at thyroid-stimulating hormone (TSH) to assess thyroid health, we believe it's critical to also measure free triiodothyronine (fT3), free thyroxine (fT4), and TPO antibodies.
You should test your thyroid function if:
- You plan to get pregnant,
- Have a history of thyroid problems or irregular periods,
- Have miscarried
- Are unable to conceive after one year of unprotected sex.
Treat Your Thyroid
Synthetic thyroxine fully replaces the thyroid gland and successfully treats the symptoms of hypothyroidism in many patients. Your physician may specify a brand name to treat your thyroid problem. The current branded forms of synthetic T4 are Synthroid®, Levoxyl®, Levothyroid®, Tirosint®, and Unithroid.®
For the few patients who do not feel completely normal taking a synthetic preparation of T4 alone, the addition of T3 (Cytomel®) may be of benefit. This drug contains the synthetic form of one thyroid hormone, T3. T3 is the active thyroid hormone that works at the cellular level to help with the delivery of oxygen and energy to cells, tissues, and glands throughout the body.
Another treatment option is Natural Desiccated Thyroid (NDT). NDT is derived from the dried (desiccated) thyroid glands of pigs or cow and provides T3, T4, and other thyroid hormones naturally found in the human thyroid gland.
Monitor Your Thyroid
Managing hypothyroidism takes time and attention. Your care team should work with you coordinate follow-up tests and appointments as necessary to get - and keep - you feeling your best.
If your thyroid returns to normal levels and you still have difficulty conceiving, it may be time to consult a fertility specialist.