Introduction:
Thyroid hormones are involved in the development of the placenta, ovary, and uterine walls during female reproduction. The thyroid hormones are tetraiodothyronine (T4) and triiodothyronine (T3). These hormones act directly on uterine, ovarian, and placental tissues to modulate the metabolism and development of these organs. They function through multiple interactions with other hormones such as prolactin (it is a hormone responsible for milk production), insulin-like growth factor, and estrogen (female reproductive hormone), influencing the release of gonadotropin-releasing hormone (GnRH - stimulates the pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the hypothalamic-pituitary-gonadal axis. Thyroid dysfunction during pregnancy is associated with reproductive disorders such as problems with ovulation, increased frequency of abortions, congenital anomalies (defects that are present at birth), and low birth weight.
How Are Thyroid Hormones Produced and Regulated?
The regulation of thyroid hormones is by the following mechanism:
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Hypothalamus is a small structure in the brain that acts as the body’s coordinating center. The hypothalamus produces thyrotropin-releasing hormone (TRH).
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The thyrotropin-releasing hormone stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary gland. The TSH stimulates the thyroid gland to produce triiodothyronine (T3) and thyroxine (T4).
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The hypothalamus regulates the amount of TSH levels in the body. When a large amount of thyroid hormones are present in the body, the hypothalamus and pituitary gland sense them and regulate the TRH release from the hypothalamus and TSH release from the pituitary gland. When there is more thyroid hormone, the hypothalamus will respond by making less thyroid-releasing hormone (TRH) and returning the thyroid hormone levels to normal.
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Low thyroid hormone levels are referred to as underactive thyroid (hypothyroidism). Thyroid hormones are produced more abundantly in hyperthyroidism, where the pituitary gland responds appropriately by making low TSH.
What Is the Significance of Thyroid Hormones in Fetal Development?
Since thyroid hormones play an essential part in normal brain development, the fetus relies on maternal thyroid hormones. Maternal thyroid function is very crucial for the neurodevelopment of the offspring and plays an important role in the neuropsychological development of children. During the initial stages of gestation, the fetus depends on the maternal thyroid function. Hypothyroidism during pregnancy is associated with low IQ (intelligence quotient) and low cognitive ability of the offspring. Thyroid hormone deficiency during pregnancy can cause irreversible changes in the fetus. Hashimoto’s thyroiditis is a condition where the immune system destroys the thyroid gland leading to decreased thyroid hormone release and thyroid function. Women with Hashimoto’s thyroiditis have shown miscarriage and babies with stillbirth.
How Does Hyperthyroidism Affect Pregnancy?
Pregnant women with hyperthyroidism have a high risk of developing hypertension (high blood pressure), leading to pre-eclampsia and fetal loss. Pre-eclampsia is characterized by elevated blood pressure midway through pregnancy, usually after 20 weeks. It can occur earlier but most commonly occurs in late pregnancy. Women with normal blood pressure experience a sudden spike in blood pressure when they are 20 weeks or more than 20 weeks pregnant. Women with diabetes or obesity are at higher risk of developing pre-eclampsia. It also affects the lower socio-economic populations more. Premature babies are at risk for complications like low birth weight and respiratory problems. High blood pressure decreases the blood supply to the baby, which may cause less oxygen and nutrients. It affects the placenta, impairs liver function, and causes lung fluid accumulation.
Uncontrolled hyperthyroidism can cause preterm birth (birth before 37 weeks of pregnancy), low birth weight, and increased blood pressure in pregnant women.
In Grave’s disease, the thyroid gland makes too much thyroid hormone. It is also called an overactive thyroid, the most common cause of hyperthyroidism during pregnancy. Graves’ disease is common in young and middle-aged women. The symptoms of Grave’s disease are a fast heartbeat, high blood pressure, sleeping problems, and increased sweating than normal. During the first half of pregnancy, the disease worsens, and in the second half, it worsens again. In some cases, there is a severe form of hyperthyroidism in pregnancy. The symptoms are similar to hyperthyroidism but extreme, sudden, and severe. The common symptoms include:
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Persistent sweating.
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Agitation.
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Diarrhea.
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Unconsciousness.
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High fever.
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Racing heart rate of more than 140 beats per minute.
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Weight loss.
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Insomnia (difficulty in sleeping at night).
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Nervousness.
What Are the Diagnostic Tests for Thyroid Problems?
The different tests used to diagnose the condition are:
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Blood Tests- Thyroid functioning tests are done where the levels of thyroid hormones such as thyroxine (T4) and triiodothyronine (T3) are higher than usual, and the thyroid stimulating hormone (TSH) are very low.
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Imaging Tests- The imaging tests done to test the thyroid gland include:
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Thyroid Ultrasound- An ultrasound scan uses sound waves to create images of the thyroid gland. It is a non-invasive procedure where the doctor can see the thyroid gland on screen.
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Thyroid Scan- In thyroid scan, small amount of radioactive liquid is injected into the veins. A special camera will take images of the thyroid gland. This radioactive liquid makes certain parts of the thyroid appear bright. This technique is used to diagnose lumps, inflammation, or swelling in the thyroid gland.
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Physical Exam- The thyroid gland is tested by gently touching the thyroid outside of the neck to check whether there is a bumpy, tender, or enlarged thyroid gland. The eyes are checked for swelling, bulging, and redness. The doctor will check for signs of irregular heartbeats or rapid heartbeats. The doctor will check for moist or warm skin, and he/she might check the hands for tremors (shakiness).
Thyroid storm affects all parts of the body. The treatment begins as soon as a thyroid storm is detected. Anti-thyroid medications are given to the patient. These medications include Propylthiouracil and Methimazole, which reduce the production of thyroid hormones.
Radioactive iodine temporarily suppresses thyroid function by destroying the thyroid cells. It requires immediate and aggressive emergency treatment. If left untreated, it can cause congestive heart failure. The mortality rate is expected to be 75 % in untreated thyroid storms.
What Is the Treatment for Thyroid Problems in Pregnancy?
The treatment includes-
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Anti-thyroid Drugs - Anti-thyroid drugs, such as Propylthiouracil and Methimazole, can prevent the thyroid gland from making further hormones.
In hypothyroidism, Levothyroxine is the most common medicine used to treat an underactive thyroid. Levothyroxine is safe and effective to take during pregnancy. Do not use thyroid medicines that contain T3 hormones. These hormones are not safe during pregnancy.
Conclusion:
Maternal thyroid function is very important for fetal development. Thyroid hormones are crucial for organ development, especially the fetus's brain development during pregnancy. If the woman is diagnosed with thyroid problems, they need to take medicines during pregnancy. Anti-thyroid medicines are safe to take during pregnancy at low doses.
