This week, let’s pretend we have a different 26 year old, newly-pregnant woman sitting on the exam table in her obstetrician’s office. She is also excited about her pregnancy but she is more verbal and is telling her physician about the terrible nausea and vomiting, anxiety, difficulty sleeping, and general fatigue. The obstetrician can easily see that she seems to be suffering the normal symptoms of pregnancy but is also a bit worried that it may be something else. Even if nausea and vomiting occur in 50–80% of all pregnant women, especially between the 5th and 13th week, a good obstetrician will go a bit further to make sure it is not something more serious before suggesting a medication, or a supplement, to reduce the symptoms of nausea and vomiting.

Is it possible that this woman is experiencing something more severe than the normal, early pregnancy symptoms? Could it be hy-PO-thyroidism?

Quick Review:

As I wrote in my last blog, one of the great masqueraders for pregnant women is thyroid disease. Many of the symptoms that women experience in the early stages of pregnancy are the exact symptoms that occur with thyroid problems. Women will commonly experience fatigue, weight gain, constipation, insomnia, and lethargy. Health care providers will often reassure patients that this is normal and these symptoms are due to the hormonal and physiological changes that one expects with the early stages of a healthy pregnancy. However, one must be on the alert that these same symptoms could be representative of a much more serious underlying problem; one that could have major, negative ramifications on the pregnancy and the newborn infant. Left undiagnosed and untreated, hypothyroidism (low thyroid hormone) could result in serious, high-risk conditions during the pregnancy. Prematurity, preeclampsia, placental separation (abruption), and/or serious consequences in the child such as congenital cretinism (mental retardation, deafness, muteness).

This weeks blog will focus only on hy-PO-thyroidism. (when you have too little thyroid hormone) and its effects on pregnancy.

Just as HYPERthyroidism can be the great masquerader, so too can hy-PO-thyroidism. Symptoms often mimic a normal early pregnancy, such as weight gain and lethargy with a decrease in exercise ability. Hypothyroidism is defined as the inability to manufacture thyroid hormone by the thyroid gland. Missing this diagnosis can have grave irreversible neurological consequences for the fetus.

How frequent is HYPOthyroidism in pregnancy?

Hypothyroidism occurs in .1 to .3% of pregnancies. It can be associated with other autoimmune disorders such as diabetes. It is often a cause of difficulty in conceiving since women with this condition have difficulty ovulating.

What are the symptoms of hypothyroidism?

• fatigue
• constipation
• intolerance to cold
• muscle cramps
• hair loss
• dry skin
• carpel tunnel syndrome
• weight gain
• intellectual slowness
• voice changes (hoarseness)
• goiter
• insomnia
• lethargy or decrease in exercise capacity
• prolonged relaxation of deep tendon reflexes
• concentration difficulties

What are the dangers to the mother and fetus with untreated hypothyroidism?

• preeclampsia
• low birth weight
• placental abruption
• intrauterine growth restriction
• congenital cretinism (growth failure, mental retardation, deafness, muteness)
• miscarriage
• prematurity
• stillbirth
• postpartum hemorrhage

What are some of the causes of hypothyroidism?

The most common cause of hypothyroidism in pregnancy in the United States is Hashimoto’s thyroiditis. This is when the body produces antibodies against the thyroid gland rendering it unable to manufacture the hormone. However, the most common cause of hypothyroidism world wide is iodine deficiency. Iodine is essential for the manufacture of the hormone.

Other causes include subacute thyroiditis (viral illness of the thyroid gland), certain drugs (ferrous sulfate, phenytoin, rifampin), pituitary or hypothalamic disease, or prior treatment with radioactive iodine to treat Graves Disease (see previous blog).

How is hypothyroidism diagnosed?

The diagnosis of primary hypothyroidism in pregnancy is made by an elevated TSH (made by the pituitary) and a corresponding low thyroid hormone level (T4). One can also measure antibody levels in the thyroid hormones (antithyroglobulin, antithyroid peroxidase). Measurement of antibody levels is important because women who have antibodies are at increased risk of pregnancy complications and also increased risk of postpartum thyroid dysfunction. Women can have a goiter or large swelling in the neck area. Having one autoimmune disease increases the chance of developing another. Women with type I diabetes have a 5 to 8% chance of developing hypothyroidism during pregnancy and a 25% chance of developing postpartum thyroid disease.

How do you treat hypothyroidism?

The treatment of this disease is to replace the thyroid hormone with levothyroxine till the TSH levels are normal. Generally levels are followed each trimester of the pregnancy since the demands of pregnancy may necessitate an increase in dosage. If the cause of the hypothyroidism is due to iodine deficiency, replacement with iodine is essential not only during pregnancy but also after birth. Also, women who take iron during pregnancy due to anemia will have difficulty absorbing their thyroid hormone so these medications should be spaced at least 4 hours apart.

What is subclinical hypothyroidism?

This is a subgroup of thyroid impairment found in 2–5% of pregnant women. Generally the T4 is normal but the TSH is elevated. Subclinical hypothyroidism has been linked to faulty placental development. There is a three fold increased risk of abruption, higher miscarriage rate, and a two fold increase in the incidence of preterm birth leading to impaired neurodevelopment in the child. There is currently a great debate on whether women who present with this condition should be treated since studies have not shown a benefit with replacement. These patients should be followed after delivery because of the increased incidence of developing overt thyroid disease postpartum.

What course does pregnancy have on a women with already diagnosed thyroid disease prior to becoming pregnant?

Pregnancy has a beneficial effect on women with preexisting thyroid disease. Due to the suppression of the immune system, the antibodies found in Hashimoto’s disease decline but, immediately postpartum, there can be a resurgence with marked worsening of the condition. There can be a noticeable reduction in goiter size during the pregnancy.

What is the importance of fetal and neonatal hypothyroidism?

Congenital hypothyroidism occurs in one in 4,000 births. There can be multiple etiologies from genetic, immunologic, environmental, and drug induced causes. It is critically important not to miss this diagnosis in the infant since developmental retardation can occur if the condition goes untreated. Often infants appear normal at birth but deteriorate over several months. Infants can have severe retardation, deafness and muteness. This is the most common cause of mental retardation worldwide. If delay in treatment of congenital hypothyroidism is beyond 3 months, the chance of normal development is low. Currently there is mass neonatal screening programs for all babies in all 50 states prior to leaving the hospital.

Summary:

Hypothyroidism in pregnancy is a condition that should be recognized and treated so severe maternal and fetal complications can be avoided. If thyroid disease exists prior to pregnancy, women should be followed closely and adjustments made to medication throughout the pregnancy. Care should be taken not to miss postpartum thyroid problems which can be transient but have a tendency to reoccur in subsequent pregnancies. Thyroid dysfunction during pregnancy both overt and sub-clinical can predict later thyroid disease. There is also a corresponding six fold risk of diabetes later on in life. Please see my blog on crystal balls in pregnancy for more information on this.

On the other hand, most pregnant women and their babies will not experience significant problems if the hypothyroidism is mild to moderate and, if properly treated, the pregnancy can be expected to progress normally. When treatment is complete, most women feel much better than before their treatment and are able to do more and to enjoy the activities of their daily lives.