Thyroid Problems During Pregnancy

The thyroid gland plays an important role in ensuring a safe and comfortable pregnancy. Urban Health speaks to Dr Wong Ming, Consultant Physician and Endocrinologist at Sunway Medical Centre, to better understand thyroid changes during pregnancy:

Q: HOW DOES THE THYROID CHANGE DURING PREGNANCY?

Dr Wong: Pregnancy results in a number of hormonal and physiological changes that affect thyroid function.  The size of the thyroid gland can increase by 10-20% during pregnancy.

Q: WHAT IS THE INTERACTION BETWEEN THE THYROID FUNCTION OF THE MOTHER AND BABY?

Dr Wong: During the first 12 weeks of pregnancy, the baby is completely dependent on the mother for the thyroid hormone. After the first trimester, the baby’s thyroid starts producing its own thyroid hormone. However, the baby still relies on the mother to ingest adequate amounts of iodine, an essential element to make thyroid hormones. WHO recommends pregnant women to take 200 micrograms of iodine per day.

Q: DOES HYPERTHYROIDISM (EXCESSIVE THYROID HORMONE) HAPPEN DURING PREGNANCY?

Dr Wong: The most common cause of hyperthyroidism during pregnancy is Grave’s disease, an autoimmune condition that occurs in 1 out of 1500 pregnant women. It is a condition that needs to be taken seriously and correctly treated. Typically, it persists beyond the first trimester but becomes less severe as the pregnancy progresses.

Q: WHAT ARE THE DANGERS OF GRAVE’S HYPERTHYROIDISM?

Dr Wong: It can lead to high blood pressure, severe morning sickness, heart failure, and even a life-threatening condition called ‘thyroid storm’ in the mother. In the baby, this condition can result in miscarriage, intrauterine growth retardation, premature birth and low birth weight.

Q: WHAT ARE THE SYMPTOMS?

Dr Wong: They can be difficult to identify because they are similar to pregnancy, such as fatigue, insomnia and anxiety. However, two key symptoms are more indicative of hyperthyroidism: rapid pulse rate of more than 100/min and unexplained weight loss.

Q: WHAT ARE THE TREATMENT OPTIONS?

Dr Wong: Mild hyperthyroidism is usually monitored closely without therapy. If it is severe, anti-thyroid medications are recommended. Medications given include propylthioacil in the first trimester, carbimazole or methimazole for second and third trimester. The goal of therapy is to keep the mother’s free thyroid hormones in the high-normal range on the lowest medication dose. Thyroid function tests should be monitored closely during pregnancy.

For patients who cannot be adequately treated with oral medications, surgery is an alternative. This is rarely recommended due to the risks of surgery and anaesthesia to mother and baby.

Q: CAN A MOTHER ON ANTI-THYROID MEDICATIONS BREASTFEED?

Dr Wong: Yes, but it is important to monitor the baby’s thyroid function if high doses of medications are taken.

Q: DOES HYPOTHYROIDISM (LACK OF THYROID HORMONE) HAPPEN DURING PREGNANCY?

Dr Wong: Yes. The most common cause is an autoimmune condition known as Hashimoto’s thyroiditis..

Q: WHAT ARE THE RISKS TO THE MOTHER AND BABY?

Dr Wong: The mother may suffer from anaemia, heart failure, pregnancy-induced hypertension, post-partum bleeding or spontaneous abortion. The baby may have low-birth weight. As the thyroid hormone is critical for brain development, the baby may have cognitive and developmental abnormalities if the condition is not treated properly.

Q: WHAT ARE THE TREATMENT OPTIONS?

Dr Wong: Adequate doses of thyroid hormone known as levothyroxine should be taken to maintain normal thyroid function. Women who already have hypothyroidism before pregnancy should increase their dosage of levothyroxine by 25-50% as pregnancy increases thyroid hormone requirements. Discuss with your doctor if you are planning to have a baby.

It is important to realise that prenatal vitamins containing iron and calcium may impair the absorption of thyroid hormone from the gastrointestinal tract. Therefore, levothyroxine and prenatal vitamins should be taken separately by at least 2-3 hours.

Thyroid function tests should be monitored every 6-8 weeks during pregnancy. As soon as the child is delivered, the mother may revert to her pre-pregnancy dosage of levothyroxine.

This education material is Part 2 of an education series in conjunction with Thyroid Awareness Week in May brought to you by Merck Serono. Please consult your doctor for further information. Visit www.urbanhealth.com.my to read Part 1 titled ‘Your Thyroid: Your Friend or Foe?’. Don’t miss the next issue on ‘Thyroid & Your Heart: What’s the connection?’.

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