The Ill Effects of Hypothyroidism and Pregnancy

Hypothyroidism and pregnancy are not mutually exclusive!  However, if you’re pregnant, or planning to get pregnant, knowing a bit about how your thyroid functions in relation to pregnancy is a good idea because even women with perfectly normal thyroid function can experience thyroid problems either during or after pregnancy.

Normal Hormonal Changes During Pregnancy

Pregnancy causes a great many hormonal and physiological changes throughout the body.  Some of these affect thyroid function.  When you’re first pregnant, a hormone called human chorionic gonadotropin (hGC) produced by the placenta, helps the corpus luteum to develop.  The corpus luteum is responsible for producing progesterone to maintain the pregnancy and develop the endometrium (lining of the uterus) so it can support a growing fetus.

Human chorionic gonadotropin can also interact with TSH receptors on thyroid tissue cells to mildly increase production of thyroid hormones, notably during the first trimester when levels of hGC are highest.   This results in a mild (subclinical) form of hyperthyroidism (excess thyroid hormones).  When blood levels of thyroid hormones rise, the pituitary reduces production of TSH hormone.  Scientists are not sure why it’s necessary for hGC to get involved with thyroid hormone production like this but it may have something to do with the fetus’s requirement for maternal thyroid hormones during the first trimester.  Once hGC levels drop during the 2nd and 3rd trimester TSH production should return to normal.

Interestingly studies have also shown that women who suffer from severe morning sickness usually have higher levels of hGC than women who don’t.

Estrogen is another hormone that affects thyroid hormones during pregnancy.  It increases the level of thyroid binding proteins in blood serum.  These are the proteins that carry the thyroid hormones around the body.  Whilst the hormone molecules are bonded to the protein they’re inactive.  To become active (able to be used by the body) they must be ‘freed’ from the proteins.  When you see the terms ‘free T4’ and ‘free T3’ it is referring to hormone molecules that have been separated from their carrier proteins and are available for the body to use.  Therefore, when you’re pregnant, the amount of thyroid hormone in your blood serum increases.  However, most of it remains bonded to the transporter proteins so your actual free hormone levels remain normal.

Your thyroid gland will also enlarge slightly during pregnancy but should not be visible.  Around 10 – 15% is normal.  If you do develop a noticeably large thyroid (goiter) your doctor will probably arrange to test your thyroid function.

At around 12 weeks into gestation the fetal thyroid glands develop but they don’t start producing their own hormones until around 18 – 20 weeks.  During that time it relies on maternal thyroid hormones.  Once fetal thyroid hormone begins to happen, the fetus requires iodine which it obtains from the mother.  Therefore your dietary requirements for iodine will increase to not only support your own thyroid hormone production but also that of your unborn child.  Normal recommended dietary iodine is 150 micrograms and this usually increases to 200 micrograms during pregnancy.  In developed countries iodine deficiencies are uncommon thanks to products like iodized salt and iodine fortified foods.

Thyroid hormones are vital for the normal development of the fetal central nervous system and brain.  Shortfalls in these hormones, particularly in the first trimester before fetal thyroid hormone production begins, can cause neurological, cognitive and developmental problems in the baby.  Whilst this is more commonly associated with severe untreated maternal hypothyroidism caused by iodine deficiency, there is increasing evidence to suggest that even mild untreated hypothyroidism during pregnancy can lead to mild neurological abnormalities in the baby.

A new born screening test is now done shortly after birth in developed countries to pick up problems like congenital hypothyroidism.  If thyroid abnormalities are present, appropriate treatment as required is started as soon as possible.

Interesting Questions about Thyroid:

What is the Thyroid?

The thyroid is a small, butterfly-shaped gland just below the Adam’s apple. This gland plays a very important role in controlling the body’s metabolism, that is, how the body functions. It does this by producing thyroid hormones (T4 and T3), chemicals that travel through the blood to every part of the body. Thyroid hormones tell the body how fast to work and use energy.

The thyroid gland works like an air conditioner. If there are enough thyroid hormones in the blood, the gland stops making the hormones (just as an air conditioner cycles off when there is enough cool air in a house). When the body needs more thyroid hormones, the gland starts producing again.

The pituitary gland works like a thermostat, telling the thyroid when to start and stop. The pituitary sends thyroid stimulating hormone (TSH) to the thyroid to tell the gland what to do.

About 20 million Americans have some form of thyroid disease. Many are undiagnosed or misdiagnosed. No age, economic group, race, or sex is immune to thyroid disease.

The thyroid gland might produce too much hormone (hyperthyroidism), making the body use energy faster than it should, or too little hormone (hypothyroidism), making the body use energy slower than it should. The gland may also become inflamed (thyroiditis) or enlarged (goiter), or develop one or more lumps (nodules).

Fact:Two of the most common thyroid diseases, Hashimoto’s thyroiditis and Graves’ disease, are autoimmune diseases and may run in families.
Fact:Hypothyroidism is 10 times more common in women than in men.
Fact:One out of five women over the age of 75 has Hashimoto’s thyroiditis, the most common cause of hypothyroidism.
Fact:Thyroid dysfunction complicates 5%-9% of all pregnancies.
Fact:About 15,000 new cases of thyroid cancer are reported each year.
Fact:One out of every 4,000 infants is born without a working thyroid gland.

How is Thyroid Disease Treated?

If you have thyroid disease, your doctor can discuss which treatment is right for you. The two basic goals for treating thyroid disease are to return thyroid hormone levels to normal and to remove potentially cancerous lumps. Treatments include radioactive iodine, antithyroid drugs, beta-blocking drugs, thyroid hormone pills, and surgery. There are several types of treatment:

  • Radioactive iodine is used to shrink a thyroid gland that has become enlarged or is producing too much hormone. It may be used on patients with hyperthyroidism, a goiter, or some cases of cancer.
  • Surgery is normally used to remove a cancer and may also be used to remove a large goiter.
  • Thyroid hormone pills are a common treatment for hypothyroidism, for patients with a goiter, and for patients who have had thyroid surgery. The pills provide the body with the right amount of thyroid hormone.
  • Anithyroid drugs and beta-blocking drugs are used to treat hyperthyroid patients.
Thyroid Hormone Pills

When are thyroid hormone pills used?

Thyroid hormone pills provide the body with the right amount of thyroid hormone when the gland is not able to produce enough by itself. The pills are frequently needed after surgery or radioactive iodine therapy.

Thyroid hormone tablets are the standard treatment for hypothyroidism. While symptoms usually get better within a few months, most patients must take the pills for the rest of their lives. This is especially true for hypothyroidism caused by Hashimoto’s thyroiditis or radioactive iodine treatment.

If the entire thyroid gland has been surgically removed, thyroid hormone tablets replace the body’s own source of the hormone. If only a part of the gland has been removed, the pills may keep the remaining gland from working too hard. This decreases the chance that the thyroid gland will grow back.

How much hormone do I need?

The preferred hormone for treatment is levothyroxine (T4). You should use only the brand-name that your doctor prescribes, since generic brands may not be as reliable. Name-brand levothyroxine pills include Synthroid®, Levoxyl®, Levothroid®, Euthyrox®, and Eltroxin®.

Patients sometimes take more pills than they should, trying to speed up the treatment or lose weight. However, this can lead to hyperthyroidism and long term complications, such as osteoporosis. You should take the pills as your doctor prescribes.

At different times in your life, you may need to take different amounts of thyroid hormone. Therefore, you should see your doctor at least once a year to make sure everything is all right.

® Synthroid is a registered trademark of Knoll Pharmaceuticals.
® Levoxyl is a registered trademark of Jones Medical Industries.
® Levothroid is a registered trademark of Forest Pharmaceuticals.
® Euthyrox is a registered trademark of EM Pharma.
® Eltroxin is a registered trademark of Roberts Pharmaceuticals.

Are thyroid hormone pills needed after treatment for hyperthyroidism?
Many patients treated for hyperthyroidism become hypothyroid. They will need to take thyroid hormone pills for the rest of their lives. In addition, they will need to see their doctor at least once a year.

Have more questions? Need more answers? Check our Full Thyroid FAQ

Hypothyroidism and Pregnancy – The Risks

Generally speaking, if you have an under active thyroid you should be fine so long as you keep taking your medications.  You should nevertheless have a TSH test when your pregnancy is confirmed to ensure your current dosage is sufficient.  It’s frequently the case that dosages need to be increased during pregnancy to account for the fact that you are supplying hormones for 2 people.  You will probably need to be tested every 6 weeks or so during the first half of your pregnancy to make sure your dose is still high enough, and at least once during the last trimester.

The biggest problems with hypothyroidism and pregnancy lie with undiagnosed and untreated hypothyroidism, particularly severe hypothyroidism.  Under those circumstances, hypothyroidism can cause:

  • late pregnancy rise in blood pressure known as pre-eclampsia
  • myopathy
  • anemia
  • abnormalities in the placenta
  • miscarriage
  • still born baby
  • low birth weight of your baby
  • transient congenital hypothyroidism in the baby
  • postpartum hemorrhage
  • and, in rare cases, congestive heart failure

Hypothyroidism and Pregnancy – The Diagnosis

As with many things to do with subclinical hypothyroidism, there are differing opinions on whether or not all women should be screened for thyroid problems during pregnancy.  Part of this is due to the fact that current thyroid function tests can be easily misinterpreted and incorrect diagnoses made.  Some doctors believe it’s important to check TSH levels either just before pregnancy or upon confirmation of pregnancy.  Others may not see the need unless the woman is in one of the high-risk groups (family history of thyroid problems, has a goiter or has had previous treatment for hyperthyroidism).

Diagnosing hypothyroidism and pregnancy is a case of having blood tests done to check thyroid hormone levels.  At the same time, the doctor will be looking for antibodies to find out the underlying cause – Hashimoto’s disease, iodine deficiency etc.

If you are diagnosed with hypothyroidism, you will be put on a course of replacement thyroid hormones, typically levothyroxine, a synthetic hormone that replaces T4.  This is the safest type of hormone for your unborn baby until he or she can begin making their own.

If you have any concerns at all about your hypothyroidism and pregnancy, it’s always best to speak to your doctor.

Donna Morgan

Donna Morgan

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