Does Thyroid Affect Pregnancy?

Thyroid gland is a small butterfly shaped organ which is located in the neck. This is an endocrine gland which produces, stores and secrets two very important hormones T3 (triiodothyronine) and T4 (thyroxine). These hormones are chemical messengers for various cellular functions and mainly regulate the metabolism and energy consumption of the body, affecting all body organs and systems.

Does Thyroid Affect Pregnancy?

A normal functioning thyroid gland is essential for fertility. An under active or overactive thyroid gland can reduce your chances of getting pregnant. Thyroid function is also crucial to maintain the pregnancy.

Optimal thyroid function is essential for ovulation and regular menstrual cycles. The menstrual cycle can get disturbed if the thyroid gland is over or under active.  An overactive thyroid gland is termed as hyperthyroidism and an underactive thyroid gland is known as hypothyroidism, both conditions lead to an imbalance of thyroid hormones which is responsible for decreased chances of conception due to irregular ovulation.

Hypothyroidism and Fertility

When thyroid hormones are not produced in adequate amounts, the ovaries do not release eggs. This decreased ovulation is one of the main reasons for infertility associated with under active thyroid. Some medical conditions like certain autoimmune and pituitary disorders result in hypothyroidism and also reduce fertility. Thyroid function test is normally part of the infertility work up.

The chances of getting pregnant get better with thyroid hormone replacement therapy. If the infertility persists even after correction of hypothyroidism, further investigations and interventions are recommended.

Hyperthyroidism and Infertility

Grave’s disease is one of the most common disease which causes an overactive thyroid. The symptoms of hyperthyroidism include loss of weight, sleep disturbance, brittle hair and fine tremors of hands. Increased levels of thyroid hormones lead to a low sperm count in men and reduced period frequency in women, both of these conditions greatly reduce the chances of getting pregnant.

When Should You Test Your Thyroid?

If you are having a problem in getting pregnant and are having any of the following symptoms you need to get a full evaluation of your thyroid function as soon as possible.

  • If you have been trying to get pregnant for last six months and there is no success
  • Any history of two or more early miscarriages
  • Irregular, infrequent or excessive periods
  • Anyone in your family having thyroid problems

How does Thyroid Affect Safe Pregnancy?

Does thyroid affect pregnancy? The answer is yes, most definitely. An underactive and untreated thyroid gland puts you at a greater risk for miscarriage in early stages of pregnancy. Women who have hyperthyroidism and are not treated are also more likely to have a miscarriage.

How does Hypothyroidism Affect Pregnancy?

Metabolic demands of the body increase during pregnancy and extra thyroid hormones are required to meet the metabolic needs of the growing body and the developing baby. Normally the thyroid gland makes more hormones during pregnancy to support the baby. If a woman has already got an undiagnosed underactive thyroid gland, the hormone levels can drop significantly and there can be significant symptoms of hypothyroidism.

Symptoms of hypothyroidism

The most significant symptoms of hypothyroidism are weight gain and extreme tiredness, which can be missed, because pregnancy itself leads to both of these. Other symptoms of an underactive thyroid are:

  • Lack of concentration and memory problems
  • Constipation
  • Cramps
  • Cold intolerance

Hypothyroidism must be treated; even a mild condition can lead to serious complications during pregnancy such as miscarriage, premature birth, preeclampsia, placental abruption, and anemia. There are chances of excessive blood loss during and after delivery.


The treatment of hypothyroidism is same for pregnant and non pregnant women. The medicine Levothyroxine Sodium is prescribed which is safe to take during pregnancy. There may be some need for dose adjustment, and to do that the TSH levels are monitored and checked every six weeks to make sure they are in normal range. Iron supplements and calcium which are commonly prescribed during pregnancy can interfere with the absorption of thyroid replacement pills and they should not be taken at the same time. Your doctor will guide you regarding the best time to take your medicines.

How does Hyperthyroidism Affect Pregnancy?

Does thyroid affect pregnancy? Yes, pregnant women with untreated hyperthyroidism are at a greater risk of having a premature birth or still birth. There are also more chances of the baby having a low birth weight or a very fast pulse (Fetal tachycardia). In hyperthyroidism resulting from Grave’s disease, there are thyroid stimulating antibodies in the blood. These antibodies are able to cross the placental barrier and when they enter the baby’s system they can lead to over stimulation of thyroid gland and the baby can have hyperthyroidism at birth.

Some of the very serious complications of untreated hyperthyroidism during pregnancy are early miscarriage, congestive heart failure, anemia and preeclampsia. Another rare but life threatening condition is known as thyroid storm.

Symptoms of hyperthyroidism

The symptoms of hyperthyroidism like fatigue, heat sensitivity and fast heart rate are very similar to those of normal pregnancy and can be missed. Other symptoms are:

  • Nervousness and anxiety
  • Trembling hands
  • Irregular pulse
  • Sleep disturbance
  • Weight loss
  • Severe nausea and vomiting


It can be challenging to treat hyperthyroidism during pregnancy because of the various side effects of radioactive iodine, which is the drug of choice for hyperthyroidism treatment. It crosses the placenta and can seriously damage the baby’s thyroid gland leading to hypothyroidism.

If the condition is very mild, no medicine is given and the hormone levels are closely monitored. In case the condition is severe and treatment is required, minimum doses are prescribed to keep the TSH level low, and T3 and T4 levels just around the upper limit of the normal value. The dose of medicine is adjusted accordingly to protect the developing thyroid gland of the baby.

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