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OVERACTIVITY OF THE THYROID GLAND DURING PREGNANCY

What is the thyroid gland?
What is overactivity of the thyroid gland in pregnancy?
What happens when the thyroid gland becomes overactive?
What effect does overactivity of the thyroid have on my baby?
What causes overactivity of the thyroid gland?
How is overactivity of the thyroid gland diagnosed?
How is overactivity of the thyroid gland treated?
What effect does PTU and carbimazole have on my baby?
Could my baby develop an overactive thyroid like me?
Will I be able to breast feed my baby whilst taking thyroid blocking medication?
What does thyroid surgery involve?

What is the thyroid gland?

The thyroid gland is located in the neck alongside the Adams apple. It releases thyroid hormones into the blood which power the cells of the body. The thyroid gland is controlled by another gland found in the brain known as the pituitary gland.

What is overactivity of the thyroid gland in pregnancy?

Overactivity of the thyroid gland is also called thyrotoxicosis or hyperthyroidism. Overactivity of the thyroid gland occurs in approximately 2 in every thousand pregnancies.

What happens when the thyroid gland becomes overactive?

When the gland becomes overactive the thyroid gland produces extra thyroid hormones which is a bit like a car being in overdrive. When the thyroid gland is overactive you may experience a number of symptoms. Some of the more common symptoms are listed below

Loss of energy
Nervousness, agitation, irritability
Sweating, dislike of heat
Tremor
Weight loss
Palpitations or fast heart rate
Diarrhoea
Muscle Weakness
Skin Changes
Swelling in the throat
Dry gritty eyes, painful or protruding eyes
Double Vision

Each patient is different and you may experience only a few of these symptoms

What effect does overactivity of the thyroid have on my baby?

If the overactivity is not well controlled you may go into early labour and your baby may be smaller than expected.

What causes overactivity of the thyroid gland?

Overactivity of the thyroid gland is usually caused by an "autoimmune condition" This means that cells which normally protect the body from infection develop a "fault" and begin to recognise the thyroid gland as foreign material and attack it. This stimulates the thyroid gland to produce extra thyroid hormones. It is not yet known why cells develop the fault that causes them to attack the thyroid gland.

How is overactivity of the thyroid gland diagnosed?

A blood test is taken to measure the level of thyroid hormones in the blood especially TSH.

How is overactivity of the thyroid gland treated?

Drug treatment or surgical removal of the thyroid gland maybe considered depending on the degree of overactivity. The medicines used to control overactivity of the thyroid gland work by blocking the production of thyroid hormones. Propylthiouracil (PTU) or carbimazole are the medicines most commonly used for this purpose. Like all medication both have side effects. These are usually mild and include skin rashes, itching and a feeling of nausea. In about 1 in 1000 patients both may cause a potentially more serious side effect whereby the white blood cells which protect against infection are no longer produced. When this occurs there is a risk of developing very severe infections. The first sign of this problem is often a very sore throat or severe mouth ulcers. If you develop either of these symptoms you should contact your GP at once.

What effect does PTU and carbimazole have on my baby?

Both drugs may pass through the placenta to your unborn baby. This in turn may cause your baby’s thyroid gland to become underactive. For this reason the specialist will monitor the therapy using the lowest dose required to control the overactive thyroid. All babies have a test of thyroid function at birth and any problems with your baby’s thyroid gland will be detected at that stage. If your baby’s thyroid gland is underactive then this is easily treated with thyroid hormones until baby recovers.

Could my baby develop an overactive thyroid like me?

Yes this is feasible. Overactive thyroid is often the result of mother producing an antibody (protein) in the blood which switches the thyroid into an overactive mode. This antibody called Thyroid Receptor antibody (TRAB) can pass across the placenta to the baby and cause your baby to become thyroid overactive. Here the small amount of PTU or carbimazole which passes to the unborn baby from mother can be useful in controlling baby’s overactive thyroid. When baby is born then baby’s neonatal hyperthyroidism may need treated with carbimazole or PTU for three months until the antibody disappears from baby’s blood stream.This however is not common and most babyies are healthy when born, so don’t get worried!

Will I be able to breast feed my baby whilst taking thyroid blocking medication?

Thyroid blocking drugs are passed into your milk in small quantities and therefore breast feeding is not recommended. Discuss this with the specialist if you are eager to breast feed for it may be possible for you to come off therapy for a short while under specialist supervision.

What does thyroid surgery involve?

This involves removal the thyroid gland. ( see Thyroidectomy leaflet) Sometimes this type of treatment may damage the parathyroid glands which control calcium levels in the blood and found in the vicinity of the thyroid gland. If this occurs you may need to take calcium supplements for the rest of your life. Also long term thyroid hormone replacement medicine will be required.

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NHS Tayside; 2006; version 1.0

Disclaimer; no liability whatsoever is accepted for information given and all such information, especially with regard to drug usage (UK version provided), must be checked with a person’s health provider.