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Hypothyroidism, Hyperthyroidism And Pregnancy-Preparing For Pregnancy

The role of all glands in the human body is to secrete, that is, release, hormones into the blood stream. These hormones are chemical messengers that cause changes in the body. The thyroid is one such gland. It is located in front of the trachea (wind pipe) in the neck and is shaped rather like a butterfly. The hormone it secretes, thyroxine, has numerous effects throughout the body including regulating heart rate which ties in to its, perhaps, most widely known action the modulation of the rate at which the body uses and stores energy from food – generally referred to as the metabolism.

1. Thyroxine

The whole body is affected if the production of thyroxine is out of step with its needs. Over production of the hormone by an over active thyroid gland is called hyperthyroidism. The symptoms of this condition include weight loss (without dietary modification), inability to gain weight with additional calories, anxiety and agitation, tremor, lighter and /or shorter menstrual periods or amenorrhoea (periods stopping all together), excessive perspiration, insomnia, muscle weakness, fatigue and rapid heartbeat. People with an over active thyroid often report an unusual sensitivity to heat.

2. Hypothyroidism

Hypothyroidism refers to an under active thyroid gland, one which produces too little thyroxine to meet the body’s demands. The symptoms of this condition are rather opposite to those of hyperthyroidism. They include weight gain (without a change in diet), difficulty in losing weight even with a reduction in calories, hoarseness, unusually heavy and/or prolonged menstrual periods, depression, intolerance of the cold and constipation.

In common with sufferers of an over active thyroid gland, those whose thyroid is under active also experience fatigue and muscle weakness. If you are planning to conceive and are experiencing any of these symptoms seek a blood test from your doctor to rule out thyroid abnormalities.

Like other chronic conditions, thyroid problems may be pre-existing or may be brought on by pregnancy itself. If left undiagnosed and untreated thyroid problems can have serious consequences for the mother and baby alike. Women with thyroid problems are at increased risk of developing a form of high blood pressure late in pregnancy called pre-eclampsia. Pre-eclampsia can lead to seizures and maternal and newborn death. Women with thyroid hormone imbalances are also more likely than average to give birth prematurely.

hypothyroidism pregnancy

3. The risks to mother and baby of Hyperthyroidism in pregnancy

Younger women are more likely to be diagnosed with an over active thyroid gland than those over the age of thirty. As the condition can lead to fewer, shorter and lighter periods or them ceasing completely women with hyperthyroidism can have great difficulties conceiving. Women with an over active thyroid gland are also at greater risk of miscarriage. The anxiety and agitation that are key symptoms in the condition can be attributed to the natural feelings of uncertainty and nervousness associated with being pregnant. It is important, especially if you have a family history of thyroid hormone imbalance that your thyroid function is checked.

Women with pre-existing hyperthyroidism who are planning to conceive should ensure the condition is well managed and that, if this is done using anti-thyroid medication a possible change to a variant that is safe for use during pregnancy, such as propylthiouracil (PTU), may be recommended. Although PTU is widely considered to be the safest of this type of medicine for pregnant women to take, it can affect the baby’s thyroid gland. Women with hyperthyroidism need to be monitored closely and have regular blood tests throughout pregnancy.

Some women cannot take PTU leaving few other drugs to control their thyroid hormone imbalance that would be safe during pregnancy. In such instances a thyroidectomy, that is, surgical removal of the thyroid gland may be recommended before becoming pregnant or during pregnancy. A further option is treatment with radio-active iodine. This is not, however, a treatment that can be carried out during pregnancy due to unacceptable risk to the foetus.

4. The risks to mother and baby of Hypothyroidism in pregnancy

Just as is in the case of an over active thyroid, key symptoms of an under active thyroid are easily mistaken for normal or common features of pregnancy such as fatigue, weight gain and easily becoming overly emotional. It is well worth getting your thyroid function tested if you are planning to become pregnant, especially if you have a family history that included thyroid gland issues. Treating an under active thyroid gland during pregnancy is rather more straight forward that treating hyperthyroidism. The drug used to correct the deficit of thyroid hormone, levothyroxine, is exceptionally similar to the natural hormone produced by the gland itself and is safe to take during pregnancy.

Women with pre-existing hypothyroidism may need to, in consultation with their physician, increase the dose of levothyroxine they take during pregnancy. Blood tests to establish the correct dosage should be taken at regular intervals during pregnancy and if symptoms linked with having an under active thyroid worsen or new symptoms appear.

5. Thyroid problems can occur after pregnancy

Around one in twenty women who have recently had a baby will develop a thyroid problem, usually inflammation of the thyroid gland. Once again, symptoms of this problem, post partum thyroiditis can masquerade as symptoms of other conditions, most commonly post natal depression. The symptoms a woman will experience will depend on whether or not her thyroid gland becomes over active or under active and are the same as women with pre-existing hyperthyroidism or hypothyroidism experience. Usually, it is only the most extreme cases of post partum thyroiditis that require treatment or those that do not resolve themselves within around four months after birth.

If a woman has experienced thyroid gland problems during her pregnancy or has a pre-existing thyroid condition then the baby’s thyroid function will need to be tested shortly after birth. This is done via a blood test. This is essential to ensure the child can utilise the calories and nutrients in his or her feeds. Babies with thyroid conditions fail to thrive and it is, therefore, absolutely vital for the child’s health any problem be detected at the earliest possible opportunity.

Midwife sonographer facilitated

Consultant Led, Centre of Medical Excellence 


All articles on the blog and website are intended as information only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team.


This website was formerly Merrion Fetal Health. The clinic has undergone a rebrand and is now known as Merrion Ultrasound.