Treatment of Mild Hypothyroidism Improves Pregnancy Outcomes

pregnancy, thyroid disease, hypothyroidism

Undiagnosed or untreated overt hypothyroidism during pregnancy has been shown to increase the risk of a variety of adverse outcomes, including an increased risk of miscarriage, stillbirth, prematurity/pre-term labor, and other complications. Overt hypothyroidism typically refers to a situation where thyroid stimulating hormone (TSH) levels are 10 mIU/L and above.

Now, research has shown that treating women who have even mild or subclinical hypothyroidism–defined as TSH levels less than 10.0 mIU during pregnancy may lower the risk of premature delivery, early cesarean sections, and stillbirth.

The research findings were reported on at the Society for Endocrinology annual conference in Brighton in November 2016, and conducted by Dr. Peter Taylor of the University of Cardiff in Wales.

The study evaluated more than 13,000 women who were between 12 and 16 weeks pregnant. Within that group, 518 had mild hypothyroidism, also known as subclinical hypothyroidism. Among the women identified as having abnormal thyroid function, half were randomly given the thyroid hormone replacement drug levothyroxine, and the other half received no treatment. The researchers analyzed the rates of stillbirth, neonatal death, prematurity (delivery at less than 37 weeks), and early cesarean sections.

The research found: 

  • The women with mild hypothyroidism who were untreated were more likely to have a stillbirth than women with normal thyroid function.
  • The women with thyroid dysfunction who were treated with levothyroxine had a lower risk for early gestational age and low birth weight at delivery, as well as early cesarean sections.

    In reporting the findings of the research, Dr. Taylor said:

    Our work raises the possibility of providing real benefits from using a safe, cheap and well-established treatment by simply extending it to the number of pregnant women we treat. We should consider universal thyroid screening in pregnancy as it compared favorably in terms of cost-effectiveness with other conditions that we currently screen for.

    Dr. Taylor also told the website Endocrine Today:

    “We have indicated that there may be real benefits from correcting borderline thyroid function in pregnant women using a commonly used inexpensive drug, levothyroxine. This has important outcomes, including reducing stillbirth and prematurity, although more studies are needed. It also raises the possibility that as hypothyroidism and borderline thyroid function are common, there is a compelling argument for universal thyroid screening in pregnancy. More focus on thyroid status is needed as well as consideration of universal thyroid screening.” 

    What This Means for You

    There are a number of implications these findings have for women of childbearing age and the physicians who treat them.

    Maintain Optimal Levels Before Pregnancy

    If you are mildly hypothyroid and planning to conceive, you should be aware of official guidelines regarding your optimal TSH levels prior to pregnancy.

    According to the "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and Postpartum," your dosage of thyroid hormone replacement medication should be adjusted so that your TSH is below 2.5 mIU/L prior to conception.

    Confirm Your Pregnancy as Early as Possible

    Note that experts also advise that you to confirm your pregnancy as early as possible, and have a plan in place beforehand to increase your medication dosage as soon as you know you are pregnant. Pregnancy quickly generates a substantially increased demand for thyroid hormone, and in order to protect your pregnancy and the health of your baby, it is essential that you ensure that you have sufficient thyroid hormone throughout your pregnancy.

    The most important point is after conception and during your first trimester, when your developing baby relies fully on you for all the essential thyroid hormone that ensures the baby’s normal neurological and physical development.

    If you are diagnosed with mild or subclinical hypothyroidism during pregnancy, experts advise that you be treated with thyroid hormone replacement medication without delay. The goal is to restore your thyroid levels to normal as quickly as possible.

    Ensure That Your Physicians Are Following the Guidelines and Using the Narrower, Pregnancy-Specific TSH Reference Range

    An important fact to know is that the traditional reference range used by conventional physicians to diagnose and manage hypothyroidism is significantly narrower during your pregnancy. While many laboratories have upper reference range cutoff levels ranging from 4.0 to 6.0 mIU/L 4.5, the Guidelines recommend that during pregnancy, your TSH level in the first trimester should be maintained at a level of between 0.1 and 2.5 mIU/L, 0.2 to 3.0 mIU/L during your second trimester, and 0.3 to 3.0 mIU/L in your third trimester.


    Stagnaro-Green, Alex, et al. "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum." Thyroid. Volume 21, Number 10, 2011 (Online) 

    Taylor PN, et al. Abstract #OC6.3. Presented at: Society for Endocrinology Annual Conference; Nov. 7-9, 2016; Brighton, United Kingdom.