Thyroid disorders in pregnancy: The thyroid gland can sometimes make excess thyroid hormone (hyperthyroidism) or too little thyroid hormone (hypothyroidism) – both these states are not good if you are pregnant. Thyroid hormones play an important role in the normal and healthy development of your baby. Therefore, proper levels of thyroid hormones are important during pregnancy.

Hypothyroidism and pregnancy

During the first months of pregnancy, the fetus depends on the mother for thyroid hormones. Thyroid hormones are an integral part of normal brain development. Maternal thyroid hormone deficiency due to hypothyroidism can have irreversible effects on the fetus. Early studies showed that children born to mothers with hypothyroidism had lower IQ and psychomotor (mental and motor) development.

With proper treatment, often by increasing thyroid hormone, women with hypothyroidism can give birth to healthy, babies.

Chronic lymphocytic thyroiditis (CLT)

There is evidence to suggest an increased risk of miscarriage in patients with chronic lymphocytic thyroiditis (CLT), also known as Hashimoto’s thyroiditis.

In this condition, the immune system attacks the thyroid gland, causing thyroid damage and reduced function. Some studies have shown higher rates of stillbirth and miscarriage in pregnant women with CLT.

Iodine deficiency and thyroid function during pregnancy

Too little iodine in your body is a common cause of low thyroid hormone levels. Women consume an average of 100 micrograms of iodine per day. However, the World Health Organization recommends consuming at least 250 micrograms of iodine per day during pregnancy and breastfeeding. WHO guidelines recommend that if you are pregnant or breastfeeding, you should take a daily supplement containing 150 micrograms of iodine (the amount found in most supplements).

Talk to your prenatal health care provider if you are concerned about your iodine levels, especially if you take supplements such as pregnancy or prenatal vitamins and minerals. Your obstetrician can also advise you about the potential effects of prescription and over-the-counter medications on iodine absorption and thyroid function.

How is hypothyroidism treated during pregnancy?

Underactive thyroid (hypothyroidism) If you have an underactive thyroid, your doctor may prescribe a medicine called thyroxine. Ideally, you should take these pills before and after conception to optimize your thyroid hormone levels. You can also check your thyroid function regularly to make sure your thyroid hormone levels are in the recommended range. Untreated, low levels of thyroid hormone can lead to pregnancy complications such as premature birth, low birth weight, and miscarriage.

Hyperthyroidism and Pregnancy

Pregnancy does not appear to worsen hyperthyroidism or complicate treatment in women with the condition. Healthy thyroid glands function normally during pregnancy. Less than 1 percent of women have hyperthyroidism during pregnancy.

Causes of Hyperthyroidism during pregnancy

In general, the most common cause of hyperthyroidism in women of childbearing age is Graves’ disease which occurs in 0.2% of pregnant women. In addition to other common causes of hyperthyroidism, very high HCG levels in severe cases of morning sickness (hyperemesis gravidarum) can cause transient hyperthyroidism in early pregnancy.

How does hyperthyroidism affect pregnancy?

Uncontrolled hyperthyroidism has many consequences. This can lead to premature birth (before 37 weeks of pregnancy) and low birth weight. Some studies have shown an increased incidence of gestational hypertension (high blood pressure during pregnancy) in women with hyperthyroidism.

A severe, life-threatening form of hyperthyroidism called thyroid storm can make it difficult to get pregnant. It is a condition in which thyroid hormone levels are very high and can cause high fever, dehydration, diarrhea, fast and irregular heartbeat, shock, and death if left untreated.

Overactive thyroid (hyperthyroidism) If you have an overactive thyroid, your doctor or specialist may prescribe medications that block the production of thyroid hormones (antithyroid therapy). The most common drug used for this is propylthiouracil.

If your thyroid is overactive during pregnancy, your baby is more likely than usual to have a higher heart rate (tachycardia), be born small (small for gestational age), be born early (premature), or be stillborn.

How is thyroid disease diagnosed during pregnancy?

The correct diagnosis is based on a careful review of the history, physical examination, and laboratory tests.

Healthcare providers usually do not test your thyroid before or during pregnancy unless you are at risk for thyroid disease or have signs or symptoms of it. If you have signs or symptoms of thyroid disease, especially during pregnancy, inform your obstetrician.

Signs and symptoms of thyroid disorders can appear slowly over time. so having one does not always mean you have a thyroid problem.

Your obstetrician-gynecologist will do a physical exam and blood tests to check your thyroid status. A blood test measures the levels of thyroid hormones and thyroid-stimulating hormone (also called TSH) in your body. TSH is the hormone that tells your thyroid gland to produce thyroid hormones. If you suspect you have thyroid disease, ask your doctor for a test.

Are you at risk for thyroid disease during pregnancy?

You are at higher risk of developing hypothyroidism during pregnancy than other women if you:

• Are currently being treated for thyroid disease or have thyroid nodules or a goiter. A goiter is a swollen thyroid gland that can make your neck look swollen.
• Have a history of thyroid disease (including postpartum) or had a baby with thyroid disease
• Have a family history of autoimmune diseases such as Graves’ disease or Hashimoto’s disease.

Type 1 diabetes: Diabetes is a condition associated with high sugar (glucose) in your body. Type 1 diabetes is a type of pre-existing diabetes, meaning you have it before you get pregnant. When you have type 1 diabetes, your pancreas stops producing insulin. Insulin is a hormone that helps maintain the right amount of glucose in your body.

Radiation therapy: You have received high-dose radiation therapy to the neck or treatment for hyperthyroidism.

If you have a family history of thyroid or autoimmune disease, ask your obstetrician about the test.

Does thyroid function return to normal after giving birth?

Usually, your thyroid function returns to normal after the baby is born. However, after birth, 1 in 20 women may develop permanently irregular thyroid function (postnatal thyroiditis).

In some cases, the doctor may continue treatment with thyroid hormones until the end of the last pregnancy. If you take medications or supplements to treat hypothyroidism, contact your obstetrician after your baby is born. Be sure to tell her if you are breastfeeding or bottle feeding, as this may affect your baby.

Is there a risk to the baby after birth?

Neonatal Graves’ disease occurs in about 1 percent of babies whose mothers have or had active Graves’ disease. Babies can suffer from serious illnesses that require hospitalization and intensive care. In its most severe form, neonatal hyperthyroidism can be fatal. In milder and well-managed forms, the effects of Graves disease on the child are usually temporary. But even in the best of circumstances, a mother’s Graves disease can have lasting effects on the baby.

Neonatal Graves disease is caused by the mother’s antibodies passing through the placenta to the baby. Even in women who have received definitive therapy for their Graves disease, maternal antibodies can be present years later and continue to pose a potential risk to the fetus. Thyroid medications taken by the mother can also have temporary or permanent effects on the baby. Because of these concerns, it is very important to tell your doctor if you have or have had Graves’ disease so that you and your baby can be monitored more closely.

Bottom Line

It is always best to plan your pregnancy and consult your doctor to ensure that thyroid status and treatment are optimized before pregnancy and monitored during pregnancy. However, if this does not happen and you discover that you are pregnant, contact your obstetrician and gynecologist immediately to improve your thyroid function.

If you have thyroid problems, you can still have a healthy pregnancy and protect your baby’s health by having regular thyroid function tests and taking any medicines that your doctor prescribes.