What is Thyroid Disease and Pregnancy?
Thyroid disease is a common hormonal disorder during pregnancy, second only to diabetes. It can significantly affect the body’s normal functioning in pregnant women and can have important effects on both the mother and the baby. Studies have found that during pregnancy, the thyroid gland, which produces hormones for bodily functions, gets bigger by 10% in countries with enough iodine in their diet. In countries with less iodine, it can increase by 20% to 40%.
The production of thyroid hormones increases by about 50% during pregnancy, and the need for iodine, which the body uses to make thyroid hormones, increases similarly. Problems with the thyroid in pregnant women, like hypothyroidism, where the thyroid doesn’t produce enough hormones, or hyperthyroidism, where it produces too many, need to be closely watched and treated as needed. Sometimes pregnancy can also involve thyroid nodules or thyroid cancer, needing further medical action. This article discusses thyroid disease in pregnancy and how it’s managed.
What Causes Thyroid Disease and Pregnancy?
Hypothyroidism
Hypothyroidism is a condition that occurs when your body doesn’t produce enough thyroid hormones. During pregnancy, the main cause of hypothyroidism in areas where people have an adequate iodine intake is a chronic condition known as Hashimoto’s thyroiditis. This is an autoimmune disease where your immune system attacks your thyroid gland.
Worldwide, iodine deficiency, which is when your body doesn’t get enough of the mineral iodine, remains a common reason that pregnant women develop hypothyroidism.
Hyperthyroidism
Hyperthyroidism, on the other hand, occurs when your body produces too many thyroid hormones. During pregnancy, the most common cause of this is Graves’ disease.
Less common causes of hyperthyroidism in pregnant women include toxic multinodular goiter (when nodules or lumps in the thyroid gland produce too much thyroid hormone), toxic adenoma (a noncancerous tumor in the thyroid gland that secretes excess thyroid hormone), and thyroiditis (inflammation of the thyroid gland).
One common cause of hyperthyroidism during pregnancy, affecting 1-3% of pregnant women in their first half of pregnancy, is known as transient gestational thyrotoxicosis. This is caused by increased levels of the hormone hCG, which can stimulate the thyroid gland.
Risk Factors and Frequency for Thyroid Disease and Pregnancy
During pregnancy, around 2% to 3% of women experience hypothyroidism. This is a condition where the thyroid doesn’t produce enough hormones. Among these, about 0.3% to 0.5% have obvious hypothyroidism symptoms, which is referred to as overt hypothyroidism. In contrast, 2% to 2.5% of them have hidden symptoms, known as subclinical hypothyroidism.
Less commonly, some pregnant women can develop hyperthyroidism. This is when the thyroid produces too many hormones. It affects up to 0.1% to 0.4% of pregnancies and is often referred to as overt hyperthyroidism.
Signs and Symptoms of Thyroid Disease and Pregnancy
Hypothyroidism is a condition that can also affect pregnant women, much like it does non-pregnant adults. Some women might not experience any symptoms, while others might feel tired, have constipation, gain weight, or have a lower tolerance to cold.
During a physical check-up, the doctor might notice signs such as dry skin, a swollen face, puffy eyelids, slow relaxation of muscles after exercise or activity, and a slower than normal heart rate.
Hyperthyroidism, on the other hand, is a condition that can also occur in pregnant women, the symptoms of which are the same as those in non-pregnant adults. It might cause symptoms like heart palpitations, excessive sweating, intolerance to heat, anxiety, sleeplessness, weight loss, and shaky hands.
During a physical examination, doctors might notice signs such as a faster than normal heart rate, a delay in the closing of the eyelid, excessive sweating, and overactive reflexes. If the hyperthyroidism is caused by Graves disease, there might be additional symptoms like a swollen thyroid, an abnormal protrusion of the eyes, and thick, waxy skin on the shins.
Testing for Thyroid Disease and Pregnancy
Hypothyroidism is a condition that can occur during pregnancy. It is usually identified by high TSH levels. TSH stands for “Thyroid-Stimulating Hormone,” and it’s a chemical in your blood that your brain uses to tell your thyroid gland to make more thyroid hormones. If the normal range isn’t available, a TSH level above 4.0 mU/L is generally used as the upper limit. Hypothyroidism during pregnancy may come in two forms: “overt” hypothyroidism is where your TSH is high and your free T4 (one of the thyroid hormones your body makes) is low. Alternatively, “subclinical” hypothyroidism is when TSH is high, but your free T4 level is normal.
Hyperthyroidism, which refers to an overactive thyroid, can also occur during pregnancy. Overt hyperthyroidism is identified by low TSH and high free T4 levels, whereas subclinical hyperthyroidism shows up as low TSH and normal free T4 levels. It’s important to note that a temporary form of mild (‘subclinical’) hyperthyroidism may be seen in the first three months of pregnancy. This is because changes in your body during pregnancy can alter thyroid function. This is referred to as gestational thyrotoxicosis. It reaches its peak between 7 to 11 weeks of pregnancy and happens due to the hCG hormone stimulating the TSH receptor.
Gestational thyrotoxicosis can be differentiated from a condition called Graves disease by a careful look at your medical history and examination. If you have Graves disease, TSH receptor antibodies (these are proteins made by your immune system that can affect how your thyroid gland works) will be high when tested via a blood sample.
Treatment Options for Thyroid Disease and Pregnancy
If you have hypothyroidism, a condition where your thyroid doesn’t produce enough hormones, it’s crucial that it’s treated during pregnancy. Untreated hypothyroidism can have harmful effects on both the mother and baby’s health. Hypothyroidism is often treated with thyroid hormone replacement therapy aimed at maintaining balanced thyroid-stimulating hormone (TSH) levels.
However, the treatment for a milder form of hypothyroidism, known as subclinical hypothyroidism, during pregnancy isn’t as clear because the evidence is insufficient. But the American Thyroid Association (ATA) recommends treating pregnant women with subclinical hypothyroidism if they have positive TPO antibodies and a TSH level greater than 2.5 mU/L. Thyroid function tests should be done every 4 to 6 weeks until week 20 and at least once around the 30th week of pregnancy. Typically, women already diagnosed with hypothyroidism before pregnancy may need to increase their thyroid hormone intake as the pregnancy progresses.
On the other hand, with hyperthyroidism (where the thyroid gland is overly active), the treatment goal during pregnancy is to manage mild maternal hyperthyroidism while avoiding fetal hypothyroidism. This balance is achieved by keeping maternal free T4/total T4 (types of thyroid hormones) at the upper threshold of a normal reference range using the lowest effective dose of antithyroid drugs.
Graves’ disease, a condition that causes the overproduction of thyroid hormones, is the most common cause of thyrotoxicosis (excess thyroid hormone in the body) during pregnancy. Antithyroid drugs, such as methimazole (MMI) and propylthiouracil (PTU), are commonly used to treat hyperthyroidism during pregnancy. However, during the first three months of pregnancy, MMI is avoided due to potential risks to the baby. So, PTU is the preferred first-choice medication. But in the second trimester, it’s usually switched to MMI because of the risk of liver damage associated with PTU.
If you have a situation where you can’t tolerate these antithyroid drugs or if the condition can’t be managed despite high doses, surgery might be considered. But this is rare and would typically be done in the second trimester. It’s important to note that treating the thyroid with radioactive iodine, a standard treatment for hyperthyroidism, is not recommended during pregnancy.
Subclinical hyperthyroidism and gestational thyrotoxicosis, where you might see an increased level of thyroid hormones in your blood during pregnancy, do not usually require treatment. Instead, periodic monitoring of thyroid function tests every 4 to 6 weeks is recommended to keep track of the condition.
What else can Thyroid Disease and Pregnancy be?
The process of diagnosing an overactive (hyperthyroidism) or underactive thyroid (hypothyroidism) in pregnant women is similar to the process used for adults who are not pregnant. This document doesn’t cover the detailed discussion of this process.
Possible Complications When Diagnosed with Thyroid Disease and Pregnancy
If hypothyroidism in pregnant women goes untreated, it can lead to a range of negative outcomes for both the mother and baby. These risks include premature labour, high blood pressure in pregnancy (preeclampsia), preterm delivery, hypertension during pregnancy, bleeding heavily after childbirth (postpartum hemorrhage), the baby having a low birth weight, impairment in the baby’s mental and brain development, as well as an increased likelihood of complications during birth which can lead to illness or death.
On the other hand, untreated hyperthyroidism during pregnancy also holds its own set of risks. These can include premature labour, miscarriage, the baby not growing at the normal rate in the womb, preeclampsia, low birth weight, stillbirth, and fetal abnormalities.
Potential Risks of Untreated Hypothyroidism and Hyperthyroidism During Pregnancy:
- Premature labour
- High blood pressure in pregnancy (Preeclampsia)
- Preterm delivery
- Hypertension during pregnancy
- Heavy bleeding post childbirth (Postpartum Hemorrhage)
- Baby with low birth weight
- Impairment in baby’s mental and brain development
- Increased likelihood of complications during birth leading to illness or death
- Miscarriage
- Baby not developing at the normal rate in the womb
- Stillbirth
- Fetal abnormalities
