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Thyroid and Fertility Relationship

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Fertility is defined as the ability to reproduce or to generate children.

There are many factors that affect fertility, such as age, ovulation, as well as the state of the uterus, fallopian tubes, and peritoneum for women.

In men, semen count and quality have a poor effect on fertility. Sadly, in 10% of tested couples, reasons for infertility are unknown.

Apart from these obvious reasons, infertility – which is defined as the incapacity to get pregnant or the inability to complete pregnancy towards term gestation – has also been linked with metabolic conditions, notably thyroid disorders.

After all, thyroid hormones play major roles in metabolism and many body mechanisms.

To quote the study of Verma et al as printed in the International Journal of Applied and Basic Medical Research, “Normal thyroid function is necessary for fertility, pregnancy, and to sustain a healthy pregnancy, even in the earliest days after conception.”


In hypothyroidism, the body is not able to produce the desired levels of thyroid hormones that the body needs. The lab panel of a hypothyroid person shows increased TSH levels and low free T4 levels.

As a result, the balance of chemical reactions in the body is disturbed.

An underactive thyroid is demonstrated by a number of symptoms, such as fatigue, cold insensitivity, weight gain, muscle weakness, slow heart rate, and thinning hair, to name a few.

Effects on Women’s Fertility

As it has been mentioned, the lack of thyroid hormones in the body can upset the normal balance of chemical reactions – specifically that which deals with women’s fertility.

In this condition, the following fertility disturbances can occur:

  • Anovulation – or “no ovulation,” since the ovaries are unable to release an oocyte. A disruption in the hypothalamic-pituitary-ovarian axis that normally governs this process – such as changes in thyroid hormone levels – can lead to anovulation.


  • Low levels of progesterone and estradiol, which can only be synthesized with the help of thyroid hormones. Progesterone is a hormone produced by the ovaries; it plays an important role in preparing the uterus for pregnancy. Estradiol, on the other hand, is an important form of estrogen that determines the availability of the egg to be fertilized. Estradiol affects the size and the development of the embryo. Both hormones affect fertility due to the fact low estradiol restricts ovulation, while low progesterone prevents proper embryo implantation at the uterus.


  • Decrease in the synthesis of factors VII, VIII, IX, and XI, as well as the occurrence of estrogen breakthrough bleeding. Both account for prolonged heavy menses experienced by a hypothyroid woman.


  • Luteal phase defect, which is one of the causes of infertility. This occurs when there is not enough progesterone synthesized by the ovaries, or if the uterine lining does not respond to the said hormone. As a result, the uterine lining does not thicken as it is supposed to. This makes the womb unconducive for pregnancy, as a thick uterine lining is required for the baby to attach firmly to the uterus.


  • Hyperprolactinemia, or an increase in the secretion of prolactin, a hormone that results in breastmilk production. According to a study by Dr. Dilip Gude, it occurs in 46.1% of infertile hypothyroid patients. Hyperprolactinemia interferes with fertility because it inhibits the secretion of Gonadotropin releasing hormone, which is important for the synthesis of the luteinizing hormone and follicle stimulating hormone. When both are at low levels, production of sex cells and sex steroids (hormones) are hampered.


  • Low levels of sex hormone binding globulin (SHBG), which works by binding to androgens. This leaves a high level of ‘free’ sex hormones in the body. Symptoms include menstrual irregularities, which of course affects fertility.

While it was thought that those with mild hypothyroidism were safe from such effects, studies done in 2015 have also shown that women with low-normal levels of thyroid hormone can suffer from the same degree of infertility as well.

Effects on Men’s Fertility

Hypothyroid men exhibit infertility due primarily to the effects of Hyperprolactinemia, which include the following:

  • Poor semen quality. Semen is a whitish or grayish liquid emitted by a man during ejaculation. It carries sperm, which when introduced to the female reproductive tract, can lead to conception. The normal sperm count should be at least 20 million per milliliter – 75% should be alive, 30% should be of normal shape and form, 25% should demonstrate rapid forward movement, while 50% should be swimming forward, even if at a slower rate. According to Singh et al, hyperprolactinemia affects semen quality by impairing sperm motility and altering sperm quality. If the sperm travels sluggishly – or if the other sperm die easily – chances of conception are greatly lowered.


  • Poor testicular function. The testes are oval-shaped organs located by the scrotum. They are responsible for producing sperm and testosterone, which is the primary male sex hormone. Testicular function is governed by the release of gonadotropin releasing hormone and luteinizing hormone, both of which are affected by the hyperprolactinemia that occurs in male hypothyroid patients. Expectedly, a decrease in the release of GnRH and LH lead to low testosterone levels, hormones vital for sexual functioning.


  • Disturbance in libido levels. Libido is defined as sexual desire or sexual appetite. It is hugely influenced by testosterone, a hormone produced in the testes. As it has been mentioned previously, production of the said hormone is decreased in hypothyroidism, largely due to hyperprolactinemia. As a result, loss of libido is common in men with underactive thyroids.

It is important to note that although male infertility often occurs with hypothyroidism, it can be reversed with immediate treatment and hormone supplementation.


Hyperthyroidism is a disorder where there is an increased production of thyroid hormones in the body. Also known as an overactive thyroid, it often occurs in women and in individuals aged 60 years old and above.

Hyperthyroidism is confirmed when lab panels show decreased TSH levels and increased T3 and T4 levels.

Symptoms range from heat intolerance, sleeping problems, weight loss, rapid heartrate, hand tremors, and mood swings, to name a few.

Effects on Women’s Fertility

Similar to hypothyroidism, an excess in thyroid hormones can affect a woman’s fertility status as well. A person with Graves’ disease usually experience irregular periods with light flow.

An increase in SHBG is also expected in hyperthyroid women, and this interferes with the menstrual cycle. Women with irregular menstrual cycles often find it difficult to conceive, sometimes it is a sign that no ovulation is taking place.

Sadly, about 40% of infertility cases are caused by menstrual cycle disparities.

Effects on Men’s Fertility

As for men, an overactive thyroid has been associated with erectile dysfunction, or the impairment in maintaining adequate penile erection for coitus.

This was proven in the study conducted by Dr. Giovanni Corona – results showed that hyperthyroid men were 14 to 16 times more likely to suffer from erectile dysfunction compared to euthyroid men.

The study has also shown that the lower TSH levels are (as in the case of hyperthyroidism,) the higher the man’s risk of developing erectile dysfunction.

Because of this correlation, the study recommends screening hyperthyroid men for erectile dysfunction.

Add to that, several studies have also noted that men with hyperthyroidism often exhibited decreased sperm counts.

An increase in SHBG also occurs in hyperthyroid men, and this results in more ‘inactive’ and lesser ‘active’ testosterone hormones. This brings down libido, which is vital for sexual activity that leads to conception.

Apart from influencing sexual behavior, the androgen testosterone is also vital in governing mechanisms that lead to penile erection. Low levels of testosterone cause erectile dysfunction, which, as previously stated, is common in hyperthyroid men.

Thyroid Disorder and Pregnancy

If a woman with thyroid disorder is lucky enough to get pregnant, she still cannot escape the adverse effects of the disease.

Studies show that thyroid disorders have also been associated with pregnancy risks such as pre-eclampsia, miscarriage, premature birth, poor fetal growth, and stillbirth deliveries. After all, thyroid hormones are essential in the development of the baby’s brain and nervous system.

As with the case of hypothyroidism, the lack of thyroid hormones can lead to subpar IQ and delays in normal development.

In rare cases, hyperthyroid pregnant women can expect severe morning sickness – scientifically known as Hyperemesis gravidarum. This results from increased levels of human chorionic gonadotropin during the first trimester of the pregnancy.

If left unaddressed, hyperemesis gravidarum can lead to dehydration and subsequent weight loss.

In pregnant women with Graves’ disease, the baby can be at risk of developing an overactive thyroid as well. Signs of hyperthyroidism in infants include tachycardia (fast heart rate,) poor weight gain, irritability, and premature closing of the skull sutures.


Given the thyroid hormones’ role in reproductive health, women with infertility problems and repeated miscarriages are advised to take Thyroid function tests, as thyroid disorders might be the culprit behind their reproductive concerns.

Experts recommend undergoing T3, T4, Thyroid Stimulating Hormone, and Thyroid Autoimmune testing. As for men presenting with signs of infertility, serum prolactin level determination should also be done.

Verma and her colleagues recommend that “Thyroid evaluation should be done in any woman who wants to get pregnant with family history of thyroid problem or irregular menstrual cycle or had more than two miscarriages or is unable to conceive after 1 year of unprotected intercourse.”

The importance of early thyroid screening is echoed by Dr. Dilip Gude in his article published in the Journal of Human Reproductive Sciences. He goes to write that “Thyroid function is of paramount importance in fertility and adequate screening and treatment accordingly can improve conception and delivery rates apart from overall health.”


Although hypothyroidism and hyperthyroidism are known to affect fertility, they can be reversed with treatment. For one, supplementation in hypothyroid women can help normalize ovulatory activities, as well as prolactin levels.

Proper treatment has been known to improve fertility rates as well. In fact, a study by Verma et al. has shown that those with hypothyroidism were able to conceive within 6 weeks to 1 year of treatment.

Thyroid treatment has also been proven effective in reversing infertility-related symptoms brought about by thyroid dysfunctions. A study by Krassas et al has shown that men with erectile dysfunction demonstrated an increase in SHIM scores (a tool used to assess erectile dysfunction in men) following thyroid treatment.

Women with thyroid disorders who are able to conceive can be treated while they are pregnant, contrary to popular beliefs. It is deemed safe – and doctors prescribe levothyroxine for hypothyroid women and propylthiouracil for hyperthyroid patients.

Like other medications, they pose a risk to the baby’s health, but this is minimized as long as the dose is rightly adjusted according to the woman’s weight. Additionally, the therapeutic levels need to be monitored through periodic blood tests.

With appropriate treatment, a woman with thyroid disorder can reduce adverse fetal outcomes, as well as minimize her risk for miscarriages in the future.

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