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Thyroid Series (Part 3): Menstrual Cycle & Fertility

Updated: Nov 1, 2023


Welcome to Part 3 of our Thyroid Series! In this blog, we will examine the thyroid changes that occur during your menstrual cycle and how they affect fertility.


I like to refer to the menstrual cycle as a woman's 5th vital sign because it tells us so much about our health. Let's dive in and discuss our hormones and their effects on the body that play a role in the menstrual cycle.



What changes occur in the body during a menstrual cycle?

The first day of your menstrual cycle is the first day of your period, and this begins the follicular phase of your menstrual cycle. The follicular phase is the time before the egg is released (ovulation). Surges of the hormones, estrogen, routinizing, hormone, and progesterone, or what signal the ovary to release an egg.


Once that egg is released, we enter the luteal phase where we then see a surge of progesterone. This delicate balance of hormones is what makes up the menstrual cycle. The surge of estrogen towards the middle of the cycle also stimulates the release of TSH (thyroid stimulating hormone). The luteal phase is the period in which, if the egg is fertilized by sperm, the egg implants in the uterus, and starts developing, which eventually becomes the baby.

How does your thyroid affect your menstrual cycle?

Too much or too little thyroid hormone can cause periods to be light, heavy, or irregular by affecting these hormones. Hypothyroidism tends to slow down bodily functions, which can cause periods to be very heavy. On the contrary, hyperthyroidism tends to speed up bodily functions, which can cause amenorrhea, which is no period at all. Hypothyroidism can cause periods to be heavier due to excessive shedding of the uterine wall. Thyroid issues can interfere with blood clotting, which will also result in heavier periods. Prolactin is an important hormone for breast milk production but also can affect the menstrual cycle and fertility. Hypothyroidism can also lead to hyperprolactinemia, which can cause thinning of the uterine wall, making it harder for the out to find it, and to implant. The light period could be a sign of this.


Oh, it may sound great to not have a period. It might indicate that your body is not balancing hormones properly and you don't have the proper hormonal drive to have your body perform a very important function. So, like I said before, the menstrual cycle is a very important tool to determine overall health.



Why does fertility decrease when experiencing thyroid problems?

Fertility is the ability to conceive a child. Thyroid issues that are present prior to pregnancy may affect fertility, making it difficult to get pregnant in the first place. Pregnancy occurs when an egg is fertilized by sperm. This forms a zygote, and in order for a healthy pregnancy to occur the zygote needs to implant into the uterus to grow.

Thyroid issues might make it harder to conceive since low thyroid hormones can delay ovulation. Early menopause, or menopause that starts before or around the age of 40, is another condition that hyperthyroidism may cause. Moreover, people with hypothyroidism or hyperthyroidism who are pregnant have an increased risk of miscarrying. Treating hypothyroidism with levothyroxine may increase ovulation and reduce the chance of miscarriage. People with hyperthyroidism are often treated with antithyroid medication during the second half of pregnancy. However, because these drugs cross the placenta, a healthcare professional must closely supervise your usage of them.

Thyroid disease can interfere with the body's ability to ovulate, as in the release of an egg. Without the release of an egg, a person cannot become pregnant. Hyper and hypothyroidism can cause the body to not even be able to ovulate in the first place, and hypothyroidism may cause the eggs to develop poorly. Hypothyroidism specifically can cause a shorter luteal phase. This means that even if the egg gets fertilized by sperm, it may not have enough time to implant properly into the uterus. Which can also make getting pregnant a little bit harder.


Heavy Periods

Keep in mind, that while hypothyroidism is one potential cause of heavy bleeding, there are many other possible causes and you should consult your OGBYN. Heavy menstrual bleeding is defined by the American College of Obstetricians and Gynecologists (ACOG) as one or more of the following:

  • Extended bleeding lasting longer than seven days

  • Changing tampons or pads during the night

  • Bleeding that soaks through one or more tampons or pads every hour for several hours in a row

  • Needing to wear more than one pad at a time to control menstrual flow

  • Blood clots in menstrual flow that are at least the size of a quarter


Infrequent Periods

Menstruation may sometimes be absent (amenorrhea) or infrequent (oligomenorrhea) due to hypothyroidism or hyperthyroidism. More people experience irregular periods. Absent or infrequent cycles can occur from high thyroid-releasing hormone (TRH) in people with hypothyroidism. The high TRH levels trigger the pituitary gland (a pea-sized organ located at the base of the brain) to release prolactin. In people with hyperthyroidism, too much thyroid hormone leads to increased SHBG, which can prevent ovulation. Excessive prolactin inhibits the ovaries' capacity to generate estrogen.


Symptoms related to reproductive health can result from reduced estrogen such as:

  • Infrequent periods

  • Absent periods

  • Abnormal milky discharge from the breasts (galactorrhea)

  • Hot flashes

  • Vaginal dryness

  • Infertility



In Summary

Your menstrual cycles may be impacted by thyroid issues. From heavy and frequent periods to irregular or nonexistent cycles, symptoms can vary widely. Thyroid hormones' effects on the generation of reproductive hormones are the cause of these symptoms.

This blog is not a substitute for medical advice. If you are experiencing any of these symptoms or believe that you may have a thyroid issue, please consult with your medical provider.



By: Dr. Megan Stavalone

Perinatal Certified Chiropractor at ANH Wellness


Disclaimer: "The information including but not limited to text, graphics, images, and other material contained on this website is for informational purposes only. No material on this site is intended to be a substitute for professional medical advice, diagnosis, or treatment."

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