1. Pregnancy
  2. Pregnancy health
  3. Complications

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Thyroid Disorders And Pregnancy: An Interview by Dr. Kenneth K. Chen

Thyroid hormones are crucial for normal development of the baby. Today Dr. Kenneth K Chen speaks about most common thyroid disorders and how they can affect pregnancy.

A pregnant woman having hypothyroidism

Thyroid disorders which are encountered during pregnancy are usually pre-existing but may also be diagnosed for the first time during pregnancy. Here are the most common thyroid disorders in pregnancy.

Hypothyroidism is quite common. In fact, it can occur in up to 1 to 10 women. And the most common cause is Hashimoto’s thyroiditis, which is a low-grade autoimmune condition which is usually hereditary. This chronic low-grade inflammation eventually leads to the gradual destruction of the thyroid gland, which leads to hypothyroidism. The symptoms are typically tiredness, unexplained weight gain, and/or cold intolerance.

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Typically, people can have this condition for quite some time, but it will not get diagnosed unless they develop symptoms that are severe enough to warrant testing. 

Often, it is picked up for the first time during pregnancy. OB-GYN doctors frequently check TSH level as part of the prenatal panel, and when it is higher than expected, the diagnosis of hypothyroidism is made. The treatment for this is levothyroxine supplements. Regular blood tests need to be ordered throughout pregnancy to ensure that the correct dosage of levothyroxine supplements is being prescribed.

Like hypothyroidism, this may be pre-existing or get diagnosed for the first time during pregnancy. The symptoms are typically irritability, heat intolerance, palpitations, tremors and/or excessive sweating.

The most common cause for younger women is a condition called Grave's disease, which is an autoimmune condition. The antibodies associated with this condition triggers an excessive release of thyroid hormone. The treatment for this is medication to block the production of thyroid hormone — the most commonly used are propylthiouracil (PTU) or methimazole.

If preexisting, this condition frequently gets better during pregnancy but may then flare up in the postpartum period. It needs to be very closely monitored by an endocrinologist throughout pregnancy. 

Other causes of hyperthyroidism include the acute phase of thyroiditis (for example, due to viral illness) or an autonomous thyroid nodule.

Although this is not particularly common, I would like to point out that thyroid cancer can get diagnosed during pregnancy as well. 

And the reason for this is that people who are pregnant see more doctors during pregnancy and thyroid nodules are often detected via routine physical examination. Neck ultrasound is ordered, which would subsequently confirm their presence.

If the ultrasound shows that the nodule looks even a bit suspicious, it is generally recommended that the patient undergoes a fine needle aspiration biopsy during pregnancy to ensure that all is fine. Occasionally, these can be postponed until the postpartum period as long as the patient is already towards the end of their pregnancy and agreeable with coming back for this test shortly after delivery.

A pregnant woman with a thyroid condition

If a thyroid condition is not well-controlled, it can definitely lead to more complications for the baby.

Let me start with hypothyroidism. If someone has profound hypothyroidism and this is not recognized early, it can definitely increase the risk for fetal complications such as pregnancy loss and preeclampsia towards the end of pregnancy, as well as detrimentally affecting the neonate’s neurological development. 

Basically, the baby’s thyroid gland is not developed until halfway through the pregnancy, at about 20 to 21 weeks of gestation. So for the first half of the pregnancy, the baby is completely dependent on the maternal thyroid status for their own needs. 

If the mother has hypothyroidism, and this is not recognized early enough, then there is a risk that the baby’s neurocognitive development will be impaired.

Now let’s talk about hyperthyroidism. If someone’s thyroid status is not well-controlled, and they continue to be hyperthyroid during the pregnancy, this could lead to an increased risk of pregnancy loss, such as intrauterine growth retardation and preeclampsia. However, the mother should be followed regularly by an endocrinologist so that the appropriate dose of antithyroid medication can be administered — an overdose of these medications could also render the baby relatively hypothyroid, which would lead to neurocognitive impairment as well as fetal goiter (enlarged thyroid gland) which could cause airway issues at the time of delivery.

Basically, neither of the above conditions are a good thing, so it is important to be tested for these conditions if experiencing any symptoms before they get pregnant. If either of these conditions are diagnosed, it is important that they be well-controlled prior to conception in order to minimize any potential complications.  

If they are to experience any of the above symptoms after they fall pregnant, it is important that they bring them to their OB-GYN’s attention straight away so that they can be checked for these conditions and if positive, be referred to specialists for the appropriate treatment.

It’s important to be aware of a thyroid condition called postpartum thyroiditis, which usually presents between 2 to 6 months postpartum. The acute phase of this is hyperthyroidism and once this settles (usually within 2-3 weeks), the person may become transiently or permanently hypothyroid. It can affect up to 1 in 10 women. The most common presentation is mood disorder and so thyroid function testing should be strongly considered in anyone who is experiencing the “postnatal blues.”  

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