What is the role of thyroid gland?

Thyroid gland is a butterfly shaped endocrine gland located in the neck. It produces thyroid hormones T3 and T4 and is controlled by TSH produced from another gland located in brain called pituitary gland.
Thyroid hormone helps in using energy, keep the body warm and maintaining the working of brain, heart, muscle and other organs in order.
Both excess (called as thyrotoxicosis) and deficiency of thyroid hormone (called as hypothyroidism) may be harmful and cause problems.

Thyroid physiology in pregnancy
Pregnancy is a time when lot of hormonal and metabolic changes are taking place in the body. Thyroid hormonal profile changes throughout the pregnancy.

Firstly, due to high estrogen hormone, increased amount of binding proteins are there, so there is increase in total T4 levels.

Secondly, an enzyme called deiodinase (that degrades thyroid hormones T3 & T4) is increased, so to compensate there is increased production of thyroid hormones.

Thirdly, high hCG in first trimester increases thyroid hormone production and decreases TSH.

Fourthly, some thyroid hormone is transferred to the baby also.

Lastly, to meet this increased requirement of thyroid hormone during pregnancy thyroid gland increases in size. If you are eating a iodine sufficient diet, then this increase is not much and you may not even notice it. But if your diet is not iodine sufficient, then it may increase by about 20-40% and may be clinically evident.

For all the above reasons, thyroid hormone levels and TSH levels are different in a pregnant and non-pregnant women.

Hyperthyroidism in pregnancy

Hyperthyroidism means your thyroid gland is pouring too much thyroid hormones T3 and T4 in your blood and consequently TSH levels are reduced.

What can cause hyperthyroidism in pregnancy?

Hyperthyroidism can be caused by any disease that can affect non-pregnant person also. Most common causes are grave’s diseases (80-85% cases) and transient gestational hyperthyroidism.

1. Grave’s disease is an autoimmune disease characterized by formation of antibodies against TSH receptor. These antibodies stimulate thyroid gland to form more thyroid hormone.
2. Gestational hyperthyroidism is transient and occurs due to hCG (hormone released from placenta). hCG leads to increased thyroid hormone synthesis. This form of hyperthyroidism is transient and resolves after first trimester.

What are the symptoms of hyperthyroidism?

Thyroid hormone helps in maintaining the pace of metabolic processes in the body. So when excess of thyroid hormone is present, all these processes speed up. Symptoms related to these are irritability, increased sweating, fast heart beat, nervousness, anxiety, tremors, insomnia ( difficulty in sleep), thin skin, hair fall, proximal muscle weakness ( difficulty in climbing stairs, getting up from squatting position, raising arm above the head), stool frequency may increase, increased hunger and you tend to lose weight despite increased food intake.

In grave’s disease, you may also have eye symptoms like redness, swelling around the eyes, irritation, gritty sensation, visual loss, bulging of eye and diplopia (double vision). Rarely skin problem in the form of lumpy red thickening on the shins may be there.

In gestational hyperthyroidism, symptoms are usually mild or absent. Patient may have hyperemesis and multiple gestation.

What can be the complications of untreated hyperthyroidism?

Uncontrolled hyperthyroidism can cause complications in both mother and the baby.
In mother, there are increased chances of premature delivery, pre-eclampsia (high blood pressure associated with complications like seizures, kidney disease, liver disease), heart failure and cesarian section.

In the baby, there are increased chances of abortion, low birth weight, premature birth, stillbirth. Also there can be hyperthyroidism in the baby due to passage of antibodies from mother in grave’s disease.

How is hyperthyroidism diagnosed?

1. Thorough history and physical examination will be done by your doctor
2. Blood tests for thyroid profile (including TSH, FT4 or total T4 and FT3 or total T3).
3. Thyroid stimulating antibodies to confirm the diagnosis of grave’s disease and find out the risk of hyperthyroidism in the baby.
4. Ultrasound neck
5. If in doubt, FNAC may be required.
6. Radioactive iodine scan is not done in pregnancy.

How is hyperthyroidism treated in pregnancy?

1. Gestational hyperthyroidism is generally self limiting. Only symptomatic treatment is required.
2. Grave’s disease- Your doctor will prescribe anti-thyroid drugs. Depending upon which trimester, it can be propylthiouracil (first trimester) or methimazole/ carbimazole (second and third trimester). Both these drugs have their own advantages and disadvatages.
3. Sometimes surgery may be required if you are allergic to drugs, or unable to control thyroid with even high doses, or you have large swelling of thyroid gland.

How is monitoring done?

1. Your doctor will get your thyroid profile done every 4-6weeks to adjust the dose of drugs
2. You may be asked to repeat thyroid stimulating antibodies if they were high during initial testing.
3. Repeated ultrasonic monitoring of your baby will be required if your TSH stimulating antibodies are positive. This is to detect features of hyperthyroidism or hypothyroidism in the baby.

What will happen after delivery?

Pregnancy is a state of immune suppression, means your grave’s may improve during pregnancy. But after delivery, there is a chance that grave’s may worsen and you may require higher doses of anti-thyroid drugs. You can continue breast feeding, it wont harm the baby. Medicine should be taken after feeding the baby.
Baby should be examined regularly for the development of hypothyroidism or hyperthyroidism.

Hypothyroidism in pregnancy

Hypothyroidism means your thyroid gland is producing less thyroid hormone that required by your body. So you will have low FT3/Total T3 and FT4/Total T4 and high TSH. It is called overt hypothyroidism when TSH is very high or raised TSH is associated with low thyroid hormone levels. Subclinical hypothyroidism means TSH is mildly raised with normal thyroid hormone levels.

What can cause hypothyroidism?

Hypothyroidism in pregnancy can be due to any disease that causes hypothyroidism in non-pregnant person. Most common cause is autoimmune (hashimoto’s thyroiditis) which means antibodies are formed against thyroid gland and they destroy the cells producing thyroid hormone. Other causes can be previous thyroid surgery for any cause, previous radioiodine therapy, congenital hypothyroidism, thyroiditis, iodine deficiency etc.

What are the symptoms of hypothyroidism?

Due to low levels of thyroid hormone, metabolic processes of body slow down. So you have fatiguability, easily get tired, cold intolerance occurs, dryness of skin, hair fall, constipation, sleepiness and depressed feeling may be present. Symptoms may be non-specific. In subclinical hypothyroidism, you are usually asymptomatic.

What are the complications of hypothyroidism in pregnancy?

Untreated hypothyroidism (usually severe) in mother can cause anemia (low hemoglobin), muscle pain and weakness, heart failure, placental problems, pre-eclampsia and post-partum haemorrhage (excessive bleeding after delivery).

Baby can have low birth weight and brain development can be impaired (in severe cases). More commonly, mild brain developmental abnormalities are present.

Who should be tested for thyroid disease in pregnancy?

In general, all pregnant women are tested for thyroid abnormalities during their initial checkup. This is done because you may not have noticed any symptoms. You should specially be tested if you have any of the following-

1. Family history of thyroid disease
2. Goitre ( thyroid swelling or enlargement)
3. Previous history of hyperthyroidism
4. Previous history of any autoimmune disease (like type 1 diabetes, celiac disease)
5. Positive antibodies against thyroid gland
6. Previous history of radiation therapy to the head and neck area
7. Age >30years
8. If you have symptoms suggestive of thyroid disease
9. History of infertility, previous abortion or miscarriage or preterm delivery
10. If you are living in an iodine deficient area

How is hypothyroidism diagnosed?

1. Blood test for FT3/Total T3, FT4/total T4 and TSh.
2. Antibodies to thyroid gland ( will not change the treatment).
3. Ultrasound neck if thyroid gland is enlarged or swollen.
4. Rarely, FNAC may be required if you have thyroid nodule or goiter.

What is the treatment of hypothyroidism?
Thyroid hormone replacement is the treatment for hypothyroidism. If you were taking levothyroxine before pregnancy also, then you may require an increase in dose. In general, you should increase it by 2 tablets per week ( take 1 tablet extra twice a week). More frequent thyroid profile testing should be done (every 6-8weeks if stable and 4 weeks if dose has been changed).

Things to be careful for while you are on thyroid hormone replacement-

1. Take it empty stomach in the morning because absorption is best at that time (as soon as you get up in the morning).
2. Don’t take any other medicine especially iron/calcium tablets for at least 2-3 hours.
3. If you forget to take it in the morning some day, take it as soon as you remember. You can take 2 tablets together also if you have missed for 1 day.
4. Monitor your thyroid profile regularly.

ALL THE BEST!!