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    Thyroid Hormones In Pregnancy

    • 4.5   (1 Votes)

    Thyroid hormones in pregnancy raise due to the added requirement by a fetus. A woman with a history of thyroid problems must go for thyroid tests. Tg, T4, T3, and TSH tests are major tests to examine thyroid conditions hypothyroidism or hyperthyroidism. Presence of iodine modifies the final test values.

    Thyroid hormones are released from the gland known as Thyroid. Thyroid hormones play a crucial role in the overall functioning of the body especially in that of a woman. The thyroid gland weighs about 15 gm. It is located in the neck at the front side, also known as Adam's apple. Thyroid Gland is solely responsible for the production of thyroid hormones in the body. Our brain gives specific signals to the thyroid gland to maintain the required levels of hormones for the proper functioning of the body. These hormones signals are sent by hypothalamus and pituitary glands in the brain. Thyroxine is a major thyroid hormone created by the thyroid gland. Due to inclusion and composition of four iodine atoms, Thyroxine is also called as T4. It enhances its effects by converting itself into T3 also known as Triiodothyronine. In T3, one iodine atom is removed automatically from T4. T3 usually occurs in the liver, brain, and other certain tissues. Another key hormone called Thyroid Stimulating Hormone (TSH) controls the production of T4 through the Thyroid gland. TSH is made by a pituitary gland, which is located at the base of the brain. The TSH levels depend upon the amount of T4 while transmitting into the bloodstream. The production of TSH stops when T4 production in the bloodstream elevates above a certain level. Thyroid and pituitary glands act like as a thermostat and a heater. They play an automatic function similar to a heater, and its thermostat. When the heat increases, then a thermostat starts working automatically. Thermostat eventually stops the heater from working and when it cools down, it automatically starts again. (1)

    In this article we will look at the below-mentioned questions to answer briefly:

    Usually, there are four fundamental hormones of Thyroid, which regulates several organs and efficient blood flow in our body. To measure these four components, four blood tests are available to measure Thyroid problems. These four blood tests comprise of TSH, T4, T3, and T4 tests, which are widely used in cases when doctors doubt the presence of any changes in the functioning of the thyroid gland. According to experts, thyroid hormones play a crucial role in fetal development and neonatal brain. Deficiency or additional composition of these hormones also develops Hypothyroidism or Hyperthyroidism condition in our body, which has to be treated on time or before it gets worse.

    Thyroid Hormones in Pregnancy

    Functioning of the thyroid during pregnancy:

    • Increased blood concentrations of T4-binding globulin (TBG): TBG refers to one of the proteins, which transfers thyroid hormones in the blood. It also has the highest level of T4 (Thyroxine) out of all hormones. Estrogen stimulates the TBG in the liver. A nominal rise in estrogen level during pregnancy induces and almost doubles the serum of TBG concentrations. (2)
    • The increase in the levels of TBG lowers the level of free T4 concentration:The process raises the TSH (Thyroid-stimulating hormone) secretion by Pituitary Gland. Moreover, it also enhances the secretion and production of Thyroid hormones. These new levels of Thyroid hormones during pregnancy forces to create a new equilibrium of certain Thyroid hormones like T4 and T3. This increase in thyroid hormones increases till 20 weeks and remains until the delivery of the baby.
    • Increase in the demand of Iodine: During pregnancy, kidneys filter more amount of Iodine for clearance. It is recommended by the World Health Organization (WHO) to intake at least 100 to 150 ug/day to 200 ug/day of iodine in the diet during pregnancy. A fair amount of iodine is required to produce fetal and maternal thyroid hormone for a healthy pregnancy.
    • Hypothyroidism or Hyperthyroidism:This is a disorder where the thyroid gland produces an insufficient or an additional amount of hormones in different cases. This is a very common imbalance of thyroid hormones which occurs in pregnant women. Fetus disease is often seen in many pregnant women and in their fetus due to hypothyroidism or hyperthyroidism. Such conditions usually result in the delayed development of a baby during pregnancy. However, both the conditions are treated and balanced through hormonal medicines. It is recommended for the women to get regular check-ups during hypothyroidism or hyperthyroidism. It is observed in many types of research that kids born to a mother, who had severe or untreated hypothyroidism or hyperthyroidism are born with a low level of Intelligence Quotient.
    • The human Chorionic Gonadotropin (hCG) Hormone: A woman undergoes several physiological changes during pregnancy. These changes affect the maternal thyroid function and thyroid hormone level. During pregnancy, the placenta produces a certain amount of human Chorionic Gonadotropin (hCG) Hormone. The hCG is also helpful in pregnancy testing and due to this, there is a proven significance of the two week wait period after infertility treatments. This hormone is similar and related to TSH. It also has an ability to bind the TSH hormone weakly to the TSH receptor present in the thyroid gland. During the first trimester of pregnancy, when the production of hCG is high, it may turn the thyroid gland and enforce it to produce an additional thyroid hormone (Thyroxine [T4] and Triiodothyronine [T3]). These hormones depend on each other, therefore this whole process prevents the production of TSH hormone. Due to the hindered production of TSH, a pregnant woman may develop some symptoms of hyperthyroidism.(3)

    It is concluded that during pregnancy, the demand for hormones increases in the thyroid gland. A pregnant woman's hormones also monitor the functioning of the fetus. A fetus acquires the ability to manage the thyroid hormones around the 12th week of pregnancy. (4)

    Testing of Thyroid in pregnancy:

    It becomes challenging to attain and sustain the pregnancy if the thyroid levels are elevated or insufficiently produced before or during pregnancy. There are several medical treatments and medicines, which may nullify the dreadful effects of thyroid at the time of ongoing pregnancy. The main problem lies in recognizing the thyroid problem in sufficient time to be treated effectively. A woman should be cautious and observe the recent adverse changes in her body including constipation, fatigue, and heat intolerance. These constitute the common reasons for an adversely affected thyroid. Evaluating these medical conditions on time saves one from severe damages which can occur inside the body. Usually, a woman with hypothyroidism found at a huge risk of miscarriage in her first trimester. Many women with mild hypothyroidism also seem to be at a menace of losing gestation until treated on time. (5)

    Testing of Thyroid in Pregnancy

    Who should be tested for the thyroid levels?

    It becomes controversial in the case of pregnancy to get tested with thyroid or not. Pregnancy in itself has similar symptoms of having inadequate thyroid levels. Many pregnant women get confused due to similar symptoms and avoid thyroid tests mistaking herself to be pregnant. The impact of thyroid disease over mother and baby is sensitive, so one should never delay in testing the same. A high risk of thyroid disease generates the chances of losing a baby or affecting its development until the time of delivery. Women who are facing certain prominent symptoms related thyroid should get their thyroid blood tests done on time. In fact, they should also get their TSH, and free Thyroxine blood tests performed. Generally, women with the following conditions are at higher risk of thyroid problems: (5)

    • Women with a history of thyroid disease or thyroid autoimmunity
    • A family history of thyroid disease
    • A woman detected with Type 1 diabetes mellitus or any other autoimmune condition

    Any woman with these conditions should inform their physician before the check-up. It is more favorable for a woman to get tested before getting pregnant or right after a positive pregnancy test.

    Types of tests of Thyroid:

    Below are the tests, which can be performed to check any imbalance of thyroid hormones in the body:
    Types of tests of Thyroid

    1. T4 TESTS:Thyroxine (T4) is a key hormone produced by the thyroid gland along with another key hormone Triiodothyronine (T3). They together help in controlling the energy rate in our body for usage. Mostly all the T4 and T3 hormones in the blood bind with protein. Whereas, all the rest of the hormones are free or unbound. These free T4 and T3 hormones are in a biologically active form of the thyroid hormone. Here, the test measures the amount of quantity of free T4 hormone in the body. A woman undergoes symptoms of Hypothyroidism such as dry skin, weight gain, cold intolerance, infrequent menstruation, and tiredness due to thyroid dysfunctioning. This happens when the thyroid gland does not generate adequate T4 and T3 (underactive thyroid) hormones. In case the thyroid gland produces excessive T4 and T3, the concerned person may encounter indications connected with an overactive thyroid (hyperthyroidism). Free T4 in a combination with the TSH test with the FT4 or FTI, precisely determines how the thyroid gland is functioning during pregnancy. (7)
    2. T3 TESTS: T3 normal range are mainly useful in diagnosing hyperthyroidism in the patients. It also helps in determining the severity of hyperthyroidism. It has been observed that the T3 normal range level in a woman having hyperthyroidism is high. There are also certain cases of hyperthyroid where, TSH is low, T3 is elevated and rest all hormones (FT4 or FTI) are normal. T3 is mostly performed along with the TSH and T4 hormone test, as it is the last test, which will become abnormal. In some pregnancies or while taking contraceptive pills, elevated levels of T4 and T3 exist in the patient. This is commonly due to increased levels of binding proteins due to estrogen. In such a situation, doctors find it appropriate to suggest the patient undergo TSH and free T4 thyroid evaluation tests.

    3. THYROID ANTIBODY TESTS:These are the proteins, which are made by our immune system to fight with foreign substances like bacteria and viruses. In rare cases, these antibodies start attacking its own cells, tissues, and substantial organs unknowingly. This condition is known as an autoimmune response. When antibodies of Thyroid start attacking itself known to be an autoimmune disorder of Thyroid. If this disorder is not treated on time, then it leads to severe health and Thyroid problems. In fact, these antibodies disorders turn out to be worse in pregnancy if not treated. This intends to harm the mother and fetus both. It is important to get tested with Thyroid antibodies during pregnancy if one ever had thyroid disease in her past. It is safe to take thyroid medications during pregnancy to cure these thyroid problems. (8)
    4. Thyroglobulin (Tg): Iodine proves to be a substantial mineral for thyroid hormone synthesis. Generally, it is observed that a lot of pregnant women suffer from the deficiency of iodine. It is also widely known that improper iodine intake is one of the major causes of poor obstetric outcomes and neuro-development of a child. However, sufficient iodine in the body will maintain the serum Tg, which does not have any longer effect on thyroid in a pregnant woman. If there is any deficiency of iodine in the body, only then the Thyroglobulin (Tg) becomes relevant.
    5. Thyroid-stimulating hormone (TSH) Test:A TSH normal range blood test measures the same hormone called Thyroid-Stimulating Hormone (TSH) and its TSH level in blood. If a woman's body starts making excessive or insufficient hormones means that the thyroid is not working appropriately. This test helps in understanding the accuracy of the functioning of the thyroid hormone. One must know if she is suffering from hyperthyroidism or hypothyroidism to get treated on time to prevent severing of the condition. (6)

      a. Hyperthyroidism:Excessive production of TSH hormone. It usually occurs in one in every 500 pregnant women and Its symptoms are:
    • Anxiety
    • Weight loss
    • Tremors in the hands
    • Increased heart rate
    • Puffiness
    • Bulging of the eyes
    • Difficulty sleeping

    b. Hypothyroidism:It has occurred due to mild or scarce production of TSH hormone. It usually appears in one in every 250 pregnant women and Its symptoms are:

    • Weight gain
    • Tiredness
    • Hair loss
    • Low tolerance for cold temperatures
    • Irregular menstrual periods
    • Constipation

    Before performing the TSH test, the concerned doctor will instruct the patient about the same. They commonly ask for complete fast (with respect to water and food) before the test to check normal TSH levels. During pregnancy, numerous thyroid changes take place. These changes are not substantial but many women usually develop certain thyroid diseases during pregnancy affecting the TSH level. In some pregnancies, hyperthyroidism, and hypothyroidism exists in the respective woman even after the delivery.


    RADIOACTIVE IODINE UPTAKE: Radioactive iodine (RAI) for a blood test is frequently useful in the effective treatment of hyperthyroidism and thyroid cancer. However, in the case of pregnancy, it causes severe harmful effects on mental retardation, fetal hypothyroidism, and increased malignancy risk in the infant. A test of pregnancy should always be tested before the treatment of thyroid in the reproductive age of women. RAI usually creates problems in regular menses cycles and future pregnancy. Therefore, women gone through RAI test are advised to avoid pregnancy until 6 to 12 months from the time of the test performed. RAI is strictly avoided during pregnancy, but sometimes merely useful in undetected pregnancy. RAI in rare cases given to pregnant women to test the movement of radioactive iodine cells and the type of disorder one is suffering from. RAI directly crosses the placenta quickly and reaches the fetus. In the 12th week of pregnancy, a fetus starts storing the iodine of its own. Fetal tissue and the thyroid gland are 2-4 times more sensitive to radioactive cells as compared to adult cells. Therefore, RAI is more harmful and destructive for the growing fetus with iodine deficiency. By estimating the quantity of radioactivity that is used by the thyroid gland, experts may conclude whether the gland is functioning normally or not. A high amount of RAIU is detected in people whose thyroid gland is overactive (hyperthyroidism), while a low RAIU is detected when the thyroid gland is underactive (hypothyroidism). (9)


    Any condition of thyroid if left untreated before pregnancy leads to hampering the ability of a woman to get pregnant, sustain pregnancy, and unexpectedly lose her pregnancy. Generally, decent numbers of adverse thyroid pregnancy conditions are treatable. The problem lies in identifying when the problem occurred in pregnancy. One must observe her health conditions and get tested regularly for her thyroid levels to take the required precautions at the right point of time. Usually, tiredness, heat intolerance, and constipation are mistaken with pregnancy symptoms, but these could be the possible symptoms of the presence or developing thyroid problems.

    Detecting a thyroid problem is important for pregnant women, and even more substantial for those who are planning to become pregnant. The hormones of thyroid are essential for brain development. At early gestation, the fetus or the growing baby gets his thyroid hormone from his mother's body. Subsequently, after 12 weeks the fetus starts developing his own thyroid gland and storing iodine. Iodine is highly essential to produce fetal and maternal thyroid hormone. A pregnant woman or a woman who is planning to get pregnant must ensure to consume a sufficient amount of prenatal vitamins. Intake of certain special vitamins helps in providing iodine to the fetus. The labels on the packaging must be checked thoroughly before consumption because all the vitamin tablets do not contain iodine in it. (10)

    Thus, thyroid hormones contribute to a great extent in the smooth functioning of a woman's body irrespective of the fact whether she is pregnant or not. To know more about pregnancy and how to cure its complication, kindly visit our website OVO fertility".com. You can also check our other blogs on several blood tests, medicines and infertility treatments on our website. You can also contact us on +918268260808 for more details on various medical treatments.


    1 Comment


    Hem Paramartha

    June 8, 2019, 3:43 p.m. 4.5

    Leave a Comment



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