Hypothyroidism in Pregnancy: What Should You Know?

Hypothyroidism in Pregnancy: What Should You Know?

Medically reviewed by

Natalie Bessom, D.O. Board-certified family medicine doctor with specialty training in nutrition, USA

Pregnancy is an exceptional period in any female’s life. Even though nearly 45% of all pregnancies in the U.S. remain unintended, more and more women decide to plan their maternity. In the medical world, this process is usually referred to as preconception.

This article will not cover typical check-ups recommended for all individuals planning to cancel their contraception to conceive a child. We aim to concentrate on the specifics of preconception in women with hypothyroidism only, reviewing all additional steps and processes they should go through to prepare for the healthiest pregnancy possible.

The best thyroid disease is the one under control before pregnancy.​

Mother’s hypothyroidism (if unmanaged) is harming the baby directly as during the first few months of pregnancy the fetus requires maternal thyroid hormones for normal nervous system development. Later, the baby will start producing the needed hormones themselves; however, the early-term thyroid hormone deficiency outcomes can not be reversed.


Early studies demonstrated that children born to mothers with uncompensated hypothyroidism during pregnancy had lower IQ, an increased risk of disabling cerebral palsy, and impaired psychomotor development. We know that these possibilities sound terrifying but do not panic – if properly treated and controlled, women with hypothyroidism can have healthy, unaffected babies.


Another important issue is that hypothyroidism may increase the risk of infertility. Even though this topic requires more high-quality studies, most evidence appears to support an association between overt thyroid dysfunction and an increased risk of infertility.


The last but not least important reason to address any thyroid-related symptoms before getting pregnant is that many thyroid disease symptoms such as fatigue, low concentration, constipation, and abnormal sensation may be mistaken for the signs of a normal pregnancy and, thus, delay needed diagnostics and treatment.

Who needs to be tested for hypothyroidism?

According to the 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum,  routine thyroid laboratory tests are not recommended for all women planning a pregnancy. However, all females which arrived for preconception consultation or their first pregnancy appointment should undergo a clinical evaluation. If any of the following risk factors are identified, testing for serum thyroid-stimulating hormone (TSH) is recommended:

  • A history of hypothyroidism/hyperthyroidism or current symptoms/signs of thyroid dysfunction
  • Known thyroid antibody positivity or the presence of a goiter
  • History of head or neck radiation or prior thyroid surgery
  • Age >30 years
  • Type 1 diabetes or other autoimmune disorders
  • History of pregnancy loss, preterm delivery, or infertility
  • Multiple prior pregnancies (≥2)
  • Family history of autoimmune thyroid disease or thyroid dysfunction
  • Morbid obesity (BMI ≥40 kg/m2)
  • Use of amiodarone or lithium, or recent administration of iodinated radiologic contrast
  • Residing in an area of known moderate to severe iodine insufficiency.

According to this guideline, when a suppressed serum TSH is detected in the first trimester of pregnancy, a medical history, physical examination, and measurement of maternal serum FT4 or TT4 concentrations should be performed. Measurement of TRAb and maternal TT3 may prove helpful in clarifying the etiology of thyrotoxicosis.

I have been diagnosed with hypothyroidism….now what?

First of all, it is essential to define the reason behind hypothyroidism before pregnancy because specific diagnostic tests (i.e., radioactive thyroid scan) and treatments (i.e., radioactive iodine ablation of the thyroid) are not safe for pregnant women.

The further strategy depends on your particular medical condition; in this article, we will only cover overt hypothyroidism in pregnancy. If detected before pregnancy, levothyroxine dose should be titrated to achieve a TSH level of 2.5 uU/ml or below before pregnancy. Also, be prepared that your doctor may decide to increase your thyroid medication dosage by 30-50% through the pregnancy and likely as soon as your pregnancy is confirmed.

Women with overt and subclinical hypothyroidism or those at risk for hypothyroidism should be monitored with a serum TSH measurement approximately every four weeks until midgestation and at least once near 30 weeks gestation.

Will I need any other tests?

American Thyroid Association does not recommend any additional maternal or fetal testing (such as serial fetal ultrasounds, antenatal testing, and/or umbilical blood sampling) beyond the measurement of maternal thyroid function unless needed due to other circumstances of pregnancy. This recommendation does not apply to women with Graves’ disease effectively treated with 131I ablation or surgical resection, who require TSH receptor antibody (TRAb) monitoring.

If you want to dig deeper than standard patient-oriented guidelines, we recommend that you take time and read the Committee Opinion of the American College of Obstetricians and Gynecologists (ACOG) and the American Society Reproductive Medicine (ASRM). This source will help you to understand the basics of the pregnancy planning process from the perspective of the doctor.


At ThyForLife, we do our utmost to provide accurate information. For detailed medical information regarding diagnosis, treatment, and general practices please consult your healthcare professional. Always listen to the advice of your healthcare provider.
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