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Hypothyroidism During Pregnancy

Reviewed by
Dr. Kristine Eule

Hypothyroidism, also called Hashimoto’s disease, is a common problem affecting between 4 and 17 percent of women of childbearing age. Women who have been diagnosed with hypothyroidism before becoming pregnant should notify their healthcare provider as soon as possible after learning of the pregnancy because the dosage of medication needed to control hypothyroidism during pregnancy may be higher than what was needed prior to pregnancy.

Untreated hypothyroidism during pregnancy can cause complications for both the mother and her unborn baby, but well-controlled hypothyroidism does not pose any significant risks. Thyroid levels in pregnant women with hypothyroidism should be measured regularly.

What Is Hypothyroidism?

The thyroid is a gland located in the neck that releases certain hormones. Hypothyroidism is an autoimmune condition caused by a thyroid gland that is not producing enough of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). When these hormones are not being produced in the right quantities, the body can experience symptoms including (but not limited to):

Hypothyroidism During Pregnancy

In pregnancy, the thyroid gland must work harder to create even more T3 and T4. In women who already have an underactive thyroid, the thyroid will not be able to meet the changing needs of the mother and the growing baby. Thankfully, hypothyroidism in pregnancy has been well studied, and the need for treatment is well understood.

Pregnant women who have not already been diagnosed with thyroid disease are routinely tested for thyroid disorders early in pregnancy. Untreated hypothyroidism during pregnancy is associated with several complications, including low birth weight, stillbirth, premature labor, and cognitive problems in the baby. Women whose hypothyroidism is treated effectively during pregnancy, however, have the same risks of these complications as women who do not have hypothyroidism.

Subclinical hypothyroidism is a milder form of the disease, and people with this type of hypothyroidism may not experience symptoms, or they may have only mild symptoms. Subclinical hypothyroidism can still have an effect on the baby and the mother, however, and can still result in complications. People with subclinical hypothyroidism have a higher risk of later developing overt hypothyroidism.

Treatment for Hypothyroidism During Pregnancy

Women who have hypothyroidism during pregnancy will most likely need to increase the dosage of their medication in order to keep their thyroid hormone levels within the normal range. The need to increase medication dosages begins early in pregnancy, making prompt treatment important.

Pregnant women with hypothyroidism will need to have their blood thyroid levels checked on a regular basis. The ATA recommends that pregnant women’s blood thyroid levels be tested every four weeks during the first half of a pregnancy and at least one more time between weeks 26 and 32. Keeping thyroid levels within the normal range can help prevent the unborn baby from developing complications associated with hypothyroidism during pregnancy, such as learning disabilities.

The timing of thyroid medication is important to its effectiveness. Thyroid medication should be taken on an empty stomach, either one hour before eating or two hours after eating. As pregnant women are often counseled to eat frequent, small meals, this can prove challenging. However, it is extremely important for pregnant women to take their medication regularly, as prescribed. Taking the medication with food is better than not taking the medication at all.

Women are often counseled not to take certain medications during pregnancy, but thyroid medications are safe and necessary to take while pregnant. Not taking this medication as directed can have significant risks for the health of the baby and the mother.

Risks of Uncontrolled Hypothyroidism During Pregnancy

Cognitive problems: Children born to women who have subclinical hypothyroidism may have an IQ (intelligence quotient) that is several points lower than that of their peers. The chance of a low IQ or a learning disorder can be as much as four times higher in children whose mothers have untreated hypothyroidism.

One study showed a seven-point average deficit in IQ in children aged 7 to 9 whose mothers were diagnosed with subclinical hypothyroidism during their pregnancy. Another study showed children aged 25 to 30 months born to mothers with subclinical hypothyroidism had poor intellectual and motor development compared to their peers.

Stillbirth: At least one study showed that hypothyroidism in pregnant women could lead to placental abruption and stillbirth. The authors recommend treatment early in pregnancy for women with hypothyroidism.

Low birth weight (LBW) or small for gestational age (SGA): Hypothyroidism has also been associated with low-birthweight babies (those that weigh less than 5 lbs. 8 oz). A low birth weight is associated with certain complications in newborns, such as birth defects, infection, and gastrointestinal and respiratory conditions. Later in life, low-birthweight babies are more likely to develop high blood pressure, diabetes, and heart disease.

Preterm delivery: Women with hypothyroidism are at an increased risk of preterm delivery (delivery before 37 weeks). Preterm babies are more at risk for breathing problems, digestive problems, jaundice, and infections than full-term babies.

Tips for Pregnant Women with Hypothyroidism

While hypothyroidism during pregnancy can pose challenges, it is a treatable condition. There is no reason a pregnant woman with hypothyroidism cannot have a healthy pregnancy and baby. There are several steps that pregnant women with hypothyroidism can take to ensure that their condition is being treated properly:

  • If you are planning a pregnancy, talk to your healthcare provider about how your hypothyroidism will be treated before, during, and after your pregnancy.
  • See your healthcare provider as soon as you know you are pregnant.
  • Ask your healthcare provider whether your medication dosages should increase during pregnancy.
  • Take your thyroid medication on an empty stomach, and as prescribed.
  • Ensure that your thyroid hormone blood levels are being tested according to ATA recommendations (every four weeks in the first half of pregnancy, once thereafter in the third trimester, and about six weeks after giving birth).
  • Ask for your blood test results and discuss with your healthcare providers whether your thyroid hormone levels meet ATA guidelines.

Medical References:

    Alexander, E. K., Marqusee, E., Lawrence, J., Jarolim, P., Fischer, G. A., Larsen, P. R. (2004). Timing and Magnitude of Increases in Levothyroxine Requirements during Pregnancy in Women with Hypothyroidism. N Engl J Med. 351(3), 241-249. Retrieved from http://content.nejm.org/cgi/content/short/351/3/241De Groot, L., Abalovich, M., Alexander, E. K., Amino, N., Barbour, L., Cobin, R. H., Eastman, C. J., Lazarus, J. H., Luton, D., Mandel, S. J., Mestman, J., Rovet, J., Sullivan, S. (2012) Management of thyroid dysfunction during pregnancy and postpartum: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 97: 2543–2565. Retrieved from http://press.endocrine.org/doi/abs/10.1210/jc.2011-2803?view=long&pmid=22869843&journalCode=jcemJacob, J. J., Aditya, K., Achint, S., Dhar, T., Avasti, K. Increased Pregnancy Losses and Poor Neonatal Outcomes in Women with First-Trimester TSH Levels between 2.5 and 4 mIU/L Compared to Euthyroid Women with TSH Less Than or Equal to 2.5. Abstract Oro4-1. Presented at The Endocrine Society 94th Annual Meeting. June 23, 2012. Retrieved from http://www.abstracts2view.com/endo/view.php?nu=ENDO12L_OR04-1Haddow, J. E., Palomaki, G. E., Allan, W. C., et al. (1999) Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child. N Engl J Med. 341(8), 549-555. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/10451459Int J Gynaecol Obstet. 2013 Dec;123(3):196-9. doi: 10.1016/j.ijgo.2013.05.025. Epub 2013 Aug 31. Optimal treatment of hypothyroidism associated with live birth in cases of previous recurrent placental abruption and stillbirth. Vanes NK, Charlesworth D, Imtiaz R, Cox P, Kilby MD, Chan SY. http://www.ncbi.nlm.nih.gov/pubmed/24055168
[Page updated June 2017]