Click here for Frequently Asked Questions on Pregnancy.

The thyroid gland commonly enlarges during normal pregnancy, hence the thyroid may become more noticeable in pregnant women. Pregnant women will also have more frequent encounters with health care providers (nurses, physicians etc) and hence the opportunity for diagnosis of thyroid disease increases. Many physicians will check thyroid function tests in pregnant women or in women planning pregnancy, and ultrasounds done in the course of evaluating the uterus or ovaries etc may also occasionally be extended to the neck and thyroid area. For these reasons, the detection of an enlarged thyroid or thyroid disease during pregnancy is not uncommon. There has been considerable new information over the last several years attesting to the importance of maintaining normal thyroid function prior to conception and during pregnancy. For an overview of the interaction between pregnancy and thyroid disease, see Thyroid disorders in pregnancy Nat Rev Endocrinol. 2012 Nov;8(11):650-8 and Thyroid disease in relation to pregnancy: a decade of change. Clin Endocrinol (Oxf). 2000 Sep;53(3):265-78. Review. For brief summaries arising from a 2004 Workshop examining the relationship between hypothyroidism and pregnancy, see Thyroid function inside and outside of pregnancy: what do we know and what don't we know? Thyroid. 2005 Jan;15(1):54-9 and Is thyroid inadequacy during gestation a risk factor for adverse pregnancy and developmental outcomes? Thyroid. 2005 Jan;15(1):60-71.

In 2007, the Endocrine Society published a detailed synopsis of Guidelines Relating to the Diagnosis and Treatment of Thyroid Disorders in Pregnant Women. These guidelines have been updated in 2012  Management of Thyroid Dysfunction during Pregnancy and Postpartum: An Endocrine Society Clinical Practice Guideline

An overview of thyroid disease testing monitoring and treatment during pregnancy is also found here Testing, Monitoring, and Treatment of Thyroid Dysfunction in Pregnancy J Clin Endocrinol Metab. 2020 Dec 22:dgaa945. doi: 10.1210/clinem/dgaa94

For patients already taking thyroid hormone, there is often an increased required for thyroid hormone during pregnancy, and the dose of the thyroxine tablet may need to be increased several times during the course of the pregnancy to keep thyroid hormone levels in the normal range. This is generally the case for patients who have had all or part of the thyroid removed surgically, or who have had radioactive iodine treatment for hyperthyroidism, but may be seen in all types of hypothyroid states.  

Current information suggests that the requirement for thyroid hormone increases rapidly during the first half of the pregnancy, often during the first 10 weeks. After 20 weeks of gestation, thyroid hormone requirements are comparatively more stable. TSH elevations may be observed as early as 4-5 weeks after conception, and an increase in L-thyroxine dose of ~47% was seen in one study of pregnant women. These findings have prompted recommendations that women with treated hypothyroidism should increase their thyroxine dose upon diagnosis of the pregnancy (two extra tablets per week, or an increased dose of 0.025-0.05 mg), and reaffirm the importance of early monitoring to maintain TSH in the normal range during the pregnancy. See Timing and magnitude of increases in levothyroxine requirements during pregnancy in women with hypothyroidism. N Engl J Med. 2004 Jul 15;351(3):241-9. and Thyroid hormone early adjustment in pregnancy (the THERAPY) trial J Clin Endocrinol Metab. 2010 Jul;95(7):3234-41 Furthermore, the available evidence suggests it is prudent to avoid low levels of thyroid hormone in the mother during the early part of pregnancy Neonatal effects of maternal hypothyroxinemia during early pregnancy. Pediatrics. 2006 Jan;117(1):161-7. Hence, women planning conception should ideally have a thyroid TSH blood test and/or discuss thyroid hormone dose requirements with their health care providers as soon as they learn that they are pregnant. Association studies link elevations in TSH levels (more than 4.5 mU/L) with a slightly increased risk of miscarriage TSH Levels and Risk of Miscarriage in Women on Long-Term Levothyroxine: A Community-Based Study J Clin Endocrinol Metab. 2014 Oct;99(10):3895-902

Similarly, adequate maternal iodine ingestion in pregnant mothers is important to ensure an adequate supply of iodine to the developing thyroid in the baby, and some guidelines recommend iodine supplementation during pregnancy and lactation (150 ug daily) to ensure levels are adequate Iodine supplementation for pregnancy and lactation-United States and Canada: recommendations of the american thyroid association. Thyroid. 2006 Oct;16(10):949-51.

For the majority of pregnant women, thyroid hormone requirements appear to stabilize by the mid portion of the pregnancy, hence additional TSH testing during the later stages of pregnancy in a stable patient is not likely to be helpful Adjustment of levothyroxine substitutive therapy in pregnant women with subclinical, overt or postablative hypothyroidism Clin Endocrinol (Oxf). 2008 Sep 2. [Epub ahead of print]

Thyroid nodules

Thyroid nodules detected during pregnancy may generally be investigated as in the non-pregnant women, with the exception that studies involving radioactive iodine or other radioactive isotopes are contraindicated. Both the normal thyroid gland, and pre-existing thyroid nodules may increase in size during  pregnancy, but the change in size of the nodules is usually modest. See The effect of pregnancy on thyroid nodule formation. J Clin Endocrinol Metab. 2002 Mar;87(3):1010-4. An approach to the diagnosis and management of nodules during pregnancy is described here Thyroid Nodules and Thyroid Cancer in the Pregnant Woman Endocrinol Metab Clin North Am. 2019 Sep;48(3):557-567


Hypothyroidism detected in a woman planning pregnancy, or in a pregnant women should be corrected with thyroxine replacement. As the course of pregnancy evolves and the pregnant woman gains weight, the dose of thyroxine may need to be increased to keep the TSH in the normal range. Thyroxine (T4) given to pregnant patients with hypothyroidism does not cross the placenta in significant quantities, is identical in structure to the thyroxine normally made by the thyroid, and is safe to take during pregnancy and during breastfeeding.

Accumulating evidence suggests that it is important to maintain normal thyroid function in the mother for optimal development of the baby.

In the Aug 1999 issue of the New England Journal of Medicine, a study reported results of neuropsychological testing (IQ tests, school performance, language and reading skills, visual and motor performance) in 62 women with varying degrees of hypothyroidism during pregnancy. There was a small but significant difference in IQ scores in children whose mothers were not treated for their hypothyroidism during pregnancy. These results reaffirmed the importance of maintaining thyroid function at a normal level in woman planning a pregnancy, and in pregnant women. As thyroid hormone requirements commonly increase during pregnancy, pregnant women taking thyroid hormone should be appropriately monitored to make sure their TSH remains in the normal range.

Although still quite controversial, some physicians and scientists have suggested that the actual level of first trimester maternal free thyroid hormone, and not just the TSH, may be an important determinant of neuropsychological development. This hypothesis remains unproven, and is derived largely from historical retrospective evidence, and not well-designed large prospective randomized studies. To review the debate, see Is neuropsychological development related to maternal hypothyroidism or to maternal hypothyroxinemia? J Clin Endocrinol Metab 2000 Nov;85(11):3975-87. Nevertheless, some studies have suggested that reductions in circulating levels of thyroid hormones in the mother during pregnancy may be associated with mild subtle defects in cognitive development n the baby Maternal Thyroid Function during Early Pregnancy and Cognitive Functioning in Early Childhood: The Generation R Study J Clin Endocrinol Metab. 2010 Jun 9. [Epub ahead of print]. Conversely, slightly higher than normal levels of thyroxine in the mother have been associated with modest reductions in birth weight in observational studies, hence it is also desirbale to avoid tyroid hormone excess during pregnancy. Maternal Thyroid Hormone Parameters during Early Pregnancy and Birth Weight: The Generation R Study J Clin Endocrinol Metab. 2012 Nov 12

A non-randomized retrospective study of maternal hypothyroidism and IQ testing in 8 year old children of previously hypothyroid mothers found an inverse relationship between the levels of TSH during pregnancy and subsequent IQ levels in children of mothers with significant hypothyroidism during pregnancy. Although this type of study lacks important controls and attributes one would like to see in a prospective study, it adds more evidence in support of maintaining normal levels of thyroid hormones in pregnant mothers. See Relation of severity of maternal hypothyroidism to cognitive development of offspring. J Med Screen. 2001;8(1):18-20.

However, not all studies have shown a correlation between maternal and neonatal thyroid function and measures of childhood cognition in infants. In a study of 300 babies,  newborn thyroid hormone (T4) concentrations within a normal physiological reference range were not associated with maternal thyroid function and did not predict cognitive outcome in a population living in an iodine sufficient area Neonatal thyroxine, maternal thyroid function, and child cognition.J Clin Endocrinol Metab. 2008 Nov 25. [Epub ahead of print]

Lazarus and colleagues carried out a randomized trial in which thyroid hormone levels were obtained from pregnant women (21,846 study participants) at or before 16 weeks gestation (mean gestational age at which blood work was done was 12 weeks, 3 days), and the women were randomized to possible intervention (thyroid hormone replacement) based on actual results of thyroid hormone tests obtained immediately at the time of testing (Group A), or simply follow up with no review of blood work and no intervention (Group B). Women in Group A with evidence for hypothyroidism were treated with 0.15 mg levothyroxine (T4) daily. The primary outcome in this study was IQ test results in babies born to all women, assessed at 3 years of age, by psychologists who had no knowledge of maternal treatment or disposition. In women with detected hypothroidism (very low T4, elevated TSH, or both) who required treatment (390)in the intervention group, their children exhibited comparable results in subsequent tests of intelligence and cognitive function compared to the children of mothers (404) in the control group who had similar levels of thyroid dysfunction but received no intervention. Hence, antenatal screening of women to detect hypothroidism, did not appear to produce a benefit as evaluated in children at 3 years of age. Whether benefit may have been detected if treatment was started earlier or children were tested at older ages remains unknown.  Antenatal thyroid screening and childhood cognitive function N Engl J Med. 2012 Feb 9;366(6):493-501

Accordingly, patients with a history of hypothyroidism, especially those taking thyroxine, should have their TSH monitored prior to and several times during pregnancy, perhaps every 8-12 weeks, or more frequently depending on the pattern of weight gain, to ensure that the TSH and levels of free thyroid hormones remain in the normal range throughout pregnancy. Some patients with a history of thyroiditis may require a bit more thyroid hormone in the postpartum period Increased Postpartum Thyroxine Replacement in Hashimoto's Thyroiditis Thyroid. 2010 Jul 8. [Epub ahead of print]. Whether all women should have thyroid hormone testing early in pregnancy remains uncertain.

The available evidence clearly supports the importance of maintaining both maternal and neonatal thyroid function in the normal range, so as to optimize intellectual and cognitive development in the fetus. A Toronto study examined the effect of neonatal hypothyroidism, its correction, and subsequent assessment of intelligence, neuropsychological functioning, memory, and achievement. The data clearly shows that early correction of neonatal hypothyroidism is associated with improved performance on several of the standardized tests employed in this study. See The Influence of Etiology and Treatment Factors on Intellectual Outcome in Congenital Hypothyroidism. J Dev Behav Pediatr. 2001 Dec;22(6):376-384.

Some data suggests that maternal levels of thyroxine during the first trimester correlate better than maternal levels of TSH with select outcomes in children, specifically expressive language delay, when studied later in children at 30 months of age. The childrens vocabulary was not formally evaluated by reported by their mothers using standardized instryuments. However whether supplementation of thyroxine in mothers with such a hormone profile (normal TSH, low thyroxine) would produce any benefit, has not been proven in a randomized clinical trial. Maternal thyroid function during early pregnancy and cognitive functioning in early childhood: the generation R study J Clin Endocrinol Metab. 2010 Sep;95(9):4227-34

Although thyroid antibodies are commonly detected in women of childbearing age that may be experiencing infertility or miscarriage, the presence or absence of thyroid antibodies does not consistently affect the future risk of miscarriage in this group of patients in all studies. See Prospective pregnancy outcome in untreated recurrent miscarriers with thyroid autoantibodies Hum Reprod 2000 Jul;15(7):1637-1639 and Thyroid peroxidase antibody in women with unexplained recurrent miscarriage: prevalence, prognostic value, and response to empirical thyroxine therapy Fertil Steril. 2012 May 22. [Epub ahead of print]

In contrast to the data obtained in normal women, patients requiring assisted reproduction assisted reproduction technology (IVF and similar interventions) who have positive thyroid antibodies may experience a higher rate of miscarriage, in one Belgian study. See Assisted reproduction and thyroid autoimmunity: an unfortunate combination? J Clin Endocrinol Metab. 2003 Sep;88(9):4149-52. Similar findings linking thyroid antibodies to miscarriage were reported in a meta-analysis of multiple studies Thyroid autoimmunity and miscarriage: a meta-analysis Clin Endocrinol (Oxf). 2010 Dec 28. doi: 10.1111/j.1365-2265.2010.03974.x. The presence of first trimester thyroid antibodies may be associated with an increased risk of preterm delivery and some complications Thyroid antibody positivity in the first trimester of pregnancy is associated with negative pregnancy outcomes J Clin Endocrinol Metab. 2011 Jun;96(6):E920-4Furthermore, in some studies, even correction of the hypothyroidism with L-thyroxine may not result in normalization of IVF outcome rates In Vitro Fertilization Pregnancy Rates in Levothyroxine-Treated Women With Hypothyroidism Compared to Women Without Thyroid Dysfunction Disorders Thyroid. 2012 Apr 27. [Epub ahead of print]

Nevertheless, this area remains controversial, and more data is needed to determine whether the observation of positive thyroid antibodies in some women with recurrent miscarriages is of clinical significance. See Thyroid antibodies and fetal loss: an evolving story. Thyroid. 2001 Jan;11(1):57-63. Review for an overview. Considerable evidence now attests to the importance of normalizing thyroid function prior to any planned pregnancy. If this is done, the outcome of the pregnancy should not be affected by the presence of the thyroid disorder. See Overt and subclinical hypothyroidism complicating pregnancy. Thyroid. 2002 Jan;12(1):63-8. Furthermore, a meta-analysis combining the results of multiple published studies concludes that there is a clear association between the presence of thyroid antibodies and the risk of miscarriage, and in 2 studies, intervention by treatment with thyroid hormone reduced miscarriage rates in these patients. See Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence BMJ. 2011 May 9;342:d2616. doi: 10.1136/bmj.d2616

For an overview of hypothyroidism, antibodies and pregnancy, see Autoimmune thyroid disease during pregnancy Lancet Diabetes Endocrinol. 2017 Dec 12. pii: S2213-8587(17)30402-3. Perhaps the largest randomized control trial to examine this issue (does the presence of thyroid antibodies in women trying to become pregnancy, with a previous history of miscarriage or infertility, somehow indicate a therapeutic opportunity to ontervene by treating with thyroid hormone?) randomized women with positive antibodies and normal thyroid function to receive placebo, or 50 ug L-thyroxine. There was no difference in fertility outcomes, rates of miscarriage, or live births, in the treatment vs. placeboa groups and adverse events were numerically higher in women randomized to thyroixine treatment.

Levothyroxine in Women with Thyroid Peroxidase Antibodies before Conception N Engl J Med. 2019 Apr 4;380(14):1316-1325

There does appear to be a modestly higher risk of pre-term birth in women with hypothyroidism defined as elevations in TSH

Association of Thyroid Function Test Abnormalities and Thyroid Autoimmunity With Preterm Birth: A Systematic Review and Meta-analysis JAMA. 2019 Aug 20;322(7):632-641


Pregnant patients with hyperthyroidism should not have a radioactive iodine uptake or thyroid scan, and may require treatment with antithyroid drugs such as propylthiouracil (PTU) or methimazole. In some centers, if Graves disease is suspected, a thyroid stimulating immunoglobulin (TSI or LATS) test (a simple blood test) is obtained to determine if the expectant mother has circulating antibodies that may cross the placenta and stimulate the baby's thyroid. These antibody tests are not absolutely required for management of pregnant women with Grave's disease, and are usually only available in research centers. 

Although methimazole is not absolutely contraindicated during pregnancy, PTU is the preferred antithyroid drug for the pregnant women.

The risk of significant thyroid problems developing in the fetus or neonate of a women with Grave's disease is extremely rare, however it is prudent to alert the physicians responsible for monitoring the pregnancy (obstetrician or family physician) about the history of thyroid disease. In some situations, pregnant women with poorly controlled hyperthyroidism or patients with drug allergies may require surgery during pregnancy. Grave's disease often gradually improves during pregnancy, allowing for a progressive reduction in the dose of antithyroid medication. Following delivery, Grave's disease may become more accentuated, requiring reinstitution of higher doses of medication. Although highly unusual, several cases of transient suppression of thyroid function in the newborn have been detected in children born to mothers with poorly controlled hyperthyroidism during pregnancy. See Maternal thyrotoxicosis causing central hypothyroidism in infants. J Paediatr Child Health. 2002 Apr;38(2):206-208  and Central congenital hypothyroidism due to gestational hyperthyroidism: detection where prevention failed. J Clin Endocrinol Metab. 2003 Dec;88(12):5851-7.

Conversely, in mothers with Graves' disease, it is possible, albeit highly unusual, for thyroid stimulating antibodies to cross the placenta from mother to baby, and potentially cause hyperthyroidism in the developing fetus in utero, as described in A case report of neonatal thyrotoxicosis due to maternal autoimmune hyperthyroidism. Adv Neonatal Care. 2003 Dec;3(6):272-285.

For an overview of Grave's disease, pregnancy, and safety of drug use and treatment, see Drug therapy for hyperthyroidism in pregnancy: safety issues for mother and fetus. Drug Saf. 2000 Sep;23(3):229-44.

Nausea, vomiting and hyperemesis gravidarum

Some women develop intractable nausea and vomiting often in the first trimester, leading to weight loss and dehydration and treatment may require hospitalization. A subset of pregnant women with nausea and vomiting may be found to have mild abnormalities in thyroid function, often a slight elevation in T4 and/or suppressed TSH. In the majority of women, supportive treatment without the use of antithyroid drug therapy results in the resolution of the nausea and vomiting and thyroid function frequently returns to normal without treatment. Some women may develop mild hyperthyroidism due to increased HCG production or increased sensitivity to HCG, a placental hormone that has weak TSH-like activity. Hyperthyroidism that presents only with nausea and vomiting often resolves by the second trimester, and is not associated with adverse outcomes. See Transient hyperthyroidism of hyperemesis gravidarum. BJOG. 2002 Jun;109(6):683-8.

Postpartum Thyroiditis

Thyroid dysfunction may develop after childbirth, and may include hyperthyroidism,  hypothyroidism, or both. For more information, see Postpartum Thyroiditis.

The Baby

The antithyroid drugs such as PTU have been used in pregnant women for decades, appear to be safe, and do cross the placenta. It is generally possible to use very small doses of PTU in pregnant woman without affecting the baby. Rarely, fetal thyroid enlargement has been reported which appears to be reversible following discontinuation of the PTU. Thyroid 1999 Nov;9(11):1111-4 Resolution of fetal goiter after discontinuation of propylthiouracil in a pregnant woman with Graves' hyperthyroidism. The antithyroid drugs are also excreted into the breast milk of nursing mothers. Less PTU crosses into breast milk than methimazole, hence many physicians prefer PTU as the drug of choice for breastfeeding women with hyperthyroidism. Nevertheless, methimazole also appears to have been used safely during pregnancy. See Thyroid function and intellectual development of children of mothers taking methimazole during pregnancy. J Endocrinol Invest. 2002 Jul-Aug;25(7):586-9.

Although many pregnant women are understandably reluctant to take drugs during pregnancy, suboptimally treated hyperthyroidism may itself be associated with adverse effects on the baby, such as low birth weight. See Effect of maternal hyperthyroidism during late pregnancy on the risk of neonatal low birth weight. Clin Endocrinol (Oxf). 2001 Mar;54(3):365-70. 

Although most pregnant or breastfeeding hyperthyroid women are managed successfully on low doses of PTU, the majority of patients treated with larger doses of PTU seem to have good outcomes and most infants have normal levels of thyroid hormones at birth, although a transient rise in TSH has been detected in a few instances. See Thyroid function in wholly breast-feeding infants whose mothers take high doses of propylthiouracil Clin Endocrinol (Oxf) 2000 Aug;53(2):177-181. Similarly, even infants of breast feeding mothers treated with methimazole appear to be fine, with no adverse impact on thyroid function tests in the infant. See Thyroid function in breast-fed infants whose mothers take high doses of methimazole. J Endocrinol Invest. 2002 Jun;25(6):493-6.

In many parts of the world, all babies are screened, as part of neonatal screening programs for congenital hypothyroidism, for thyroid function shortly after birth. Correction of hypothyroidism detected in such infants appears to result in apparently normal subsequent physical and intellectual development, however longer follow-up (Acta Paediatr Suppl 1999 Dec;88(432):88-95 Long-term neuropsychological sequelae of early-treated congenital hypothyroidism: effects in adolescence) suggests there may be evidence for mild cognitive impairment and learning disability in some of these patients. Fort an overview, see Long-term consequences of congenital hypothyroidism in the era of screening programmes. Best Pract Res Clin Endocrinol Metab. 2002 Jun;16(2):369-82.

Although trace amounts of thyroid hormone are found in breast milk, the quantities are so low so as to preclude a meaningful effect in the breastfed baby. See The quantity of thyroid hormone in human milk is too low to influence plasma thyroid hormone levels in the very preterm infant. Clin Endocrinol (Oxf). 2002 May;56(5):621-627.

In some studies, the mild cognitive impairment detected in infants born to hypothyroid mothers clearly improves with age, and becomes less clinically obvious in older infants Acta Paediatr 2000 Mar;89(3):291-5 Neurologic development of the newborn and young child in relation to maternal thyroid function. For an overview of the potential clinical scenarios that may present as a consequence of fetal exposure to decreased levels of thyroid hormone, see The potential repercussions of maternal, fetal, and neonatal hypothyroxinemia on the progeny Thyroid 2000 Oct;10(10):871-87. and J Clin Endocrinol Metab. 2017 Dec 6. doi: 10.1210/jc.2017-02171 Maternal thyroid function in early pregnancy and neuropsychological performance of the child at 5 years of age


Women who breast feed and smoke have been shown to have reduced  iodine content in breast milk, raising the theoretical possibility that the baby will be at risk for iodine deficiency, and hypothyroidism, at a critical period of brain development. Hence, these observations provide yet one more reason to avoid smoking. See Iodine nutrition in breast-fed infants is impaired by maternal smoking. J Clin Endocrinol Metab. 2004 Jan; 89(1): 181-7.

Thyroid cancer

Pregnant women with thyroid cancer should also have their TSH monitored a few times during pregnancy, as weight gain and metabolic changes of pregnancy may result in an increased requirement for thyroid hormone to keep the TSH at an appropriately suppressed level. If surgery is required during pregnancy, many specialists advocate waiting till the second trimester to try and minimize effects on the baby. Given the slow growing nature of many thyroid nodules and thyroid cancers, the physician and patient should discuss the individual pros and cons of thyroid surgery during pregnancy on an individualized case by case basis.


Patients with both hypothyroidism and hyperthyroidism may experience menstrual abnormalities and problems with ovulation. These disturbances affect a minority of patients with thyroid dysfunction. Features of autoimmune thyroid disease are more common in women with infertility than in control populations, as shown in Thyroid dysfunction and autoimmunity in infertile women. Thyroid. 2002 Nov;12(11):997-1001. Although in most patients with mild thyroid dysfunction, correction of the thyroid problem may not improve problems such as infertility or recurrent miscarriages, it seems prudent to attempt to correct thyroid problems in women planning a pregnancy. For a review of the literature, see Thyroid disease and female reproduction Fertil Steril 2000 Dec;74(6):1063-1070. In some studies, simply treating antibody+ patients undergoing IVF with thyroxine did not improve fertility outcomes Effect of Levothyroxine on Miscarriage Among Women With Normal Thyroid Function and Thyroid Autoimmunity Undergoing In Vitro Fertilization and Embryo Transfer: A Randomized Clinical Trial. JAMA. 2017 Dec 12;318(22):2190-2198


I did not know that I was pregnant and inadvertently had a thyroid scan with a radioactive isotope at 7 weeks gestation. What will happen to my baby?

Specialized unique circumstances such as these should be discussed with an endocrinologist and obstetrician. The human fetal thyroid develops between 10-12 weeks of age, hence inadvertent administration of radioactive iodine isotopes to pregnant women earlier than 8 weeks of age will not usually affect fetal thyroid development. There is very little good clinical data from studies of this problem other than occasional case reports, hence management needs to be done on an individualized basis.

I need to have a radiology procedure with contrast dye-will this harm the baby'a thyroid?

There is a very low likelihood of transient (not permanent) alterations in neonatal thyroid hormone levels in this situation Iodine contrast prior to or during pregnancy and neonatal thyroid function: a systematic review Eur J Endocrinol. 2020 Oct 1:EJE-20-0627.R1.

I just found out I have thyroid cancer and I am pregnant-when should I have my surgery?

The answer to this question may be complex and should be individualized depending on the specific clinical circumstances. In general, patients with thyroid cancers confined to the thyroid may elect to wait till successful conclusion of the pregnancy before having an operation, generally without adverse consequences, as outlined in Outcome of differentiated thyroid cancer diagnosed in pregnant women. J Clin Endocrinol Metab. 1997 Sep;82(9):2862-6. Patients with larger tumors demonstrating progressive growth may decide to have surgery during pregnancy. These types of decisions should be made following a discussion of the risks for both the mother and the baby of operating during pregnancy, or after delivery of the baby. See Optimal timing of surgery in well-differentiated thyroid carcinoma detected during pregnancy. J Surg Oncol. 2005 Aug 23;91(3):199-203 and Management of differentiated thyroid cancer diagnosed during pregnancy. Eur J Endocrinol. 1999 May;140(5):404-6

I want to have a baby in a few years time. Should I avoid radioactive iodine treatment for my Graves' disease?

Although some physicians and patients prefer to avoid radioactive iodine in young women of childbearing age, there is little scientific evidence to suggest that radioactive iodine must be avoided in such patients. The optimal treatment of such individuals depends on many factors, and specific treatment options should be discussed by each patient with her endocrinologist. Some thyroid specialists might argue that it is better to definitely treat hyperthyroidism prior to planning a pregnancy with radioactive iodine or surgery, so as to avoid the risk of relapse or the need for antithyroid medication during pregnancy.

My TSH has been borderline elevated but I feel fine, and I am trying to get pregnant. Do I need to take thyroid hormone?

Although subclinical hypothyroidism (patient feels fine but the blood tests shows mild hypothyroidism) does not invariably need to be treated in many patients, women planning a pregnancy should maintain normal levels of thyroid function both before during and after pregnancy. The risk of miscarriage appears slightly raised in hypothyroid women, and hypothyroidism may affect ovulation and ability to become pregnant, as well as placental abruption and preterm birth. See Subclinical hypothyroidism and pregnancy outcomes. Obstet Gynecol. 2005 Feb;105(2):239-45.

Furthermore, evidence from a  study published in August 1999 in the New England Journal of Medicine emphasizes the importance of normal maternal thyroid function for optimal cognitive development in the developing baby. Although it is difficult to assign a precise relationship between borderline thyroid function and problems with conception, some studies have shown a correlation between these parameters, as outlined in Thyroxine treatment modified in infertile women according to thyroxine-releasing hormone testing: 5 year follow-up of 283 women referred after exclusion of absolute causes of infertility. Hum Reprod. 2003 Apr;18(4):707-14.  Since thyroid hormone is safe and does not have adverse consequences on pregnancy or during breast feeding, even mild "borderline" hypothyroidism should be corrected in women planning pregnancy or in pregnant women.

Although the optimal precise levels of thyroid hormones during pregnancy remains unclear, some observational studies have described a slightly higher rate of pregnancy loss in women with TSH levels above 2.5 Increased Pregnancy Loss Rate in Thyroid Antibody Negative Women with TSH Levels between 2.5 and 5.0 in the First Trimester of Pregnancy J Clin Endocrinol Metab. 2010 Jun 9. [Epub ahead of print]

It is generally recommended that hypothyroidism be corrected prior to starting attempts at pregnancy. There is little evidence that an abnormal TSH before pregnancy impairs the development of the baby, as long as the hypothyroidism is detected early and corrected in the pregnant woman Maternal Thyroid Hormone Replacement Therapy Exposure and Language and Communication Skills of Offspring at 8 Years of Age JAMA Netw Open. 2019 Oct 2;2(10):e1912424

My TSH has been found to be low during pregnancy, but I feel fine-do I need treatment?

The answer to this question clearly depends on the individual patient and clinical circumstances. However, for pregnant patients with "subclinical hyperthyroidism", namely a low TSH but otherwise normal levels of thyroid hormones, there does not appear to be any significant adverse outcome, and treatment of the abnormal TSH level may not be required as described in Subclinical hyperthyroidism and pregnancy outcomes.
Obstet Gynecol. 2006 Feb;107(2):337-41

I have just had a miscarriage and my thyroid tests are abnormal. Is there a connection?

Both thyroid disease and miscarriages are common, and many women may experience both at some point. Uncontrolled hyper or hypothyroidism may be associated with a slightly increased risk of miscarriage. Furthermore, some, but not all studies show an increased prevalence of thyroid antibodies in women with recurrent miscarriage. Overall, it seems prudent to ensure that thyroid status is as normal as possible is women contemplating pregnancy. 

I am pregnant, my TSH is suppressed and my doctor says I am hyperthyroid. Do I need treatment?

The detection of a suppressed TSH with normal levels of Free T4 and Free T3 is not uncommon. Furthermore, the symptoms of pregnancy and hyperthyroidism are both non-specific and overlapping (fatigue, warmth, occasional increases in heart rate, trouble sleeping etc). In some cases, it is appropriate to monitor the blood tests and clinical status without invariably instituting antithyroid drug therapy. In other instances, if the physician is concerned that the patient is actually hyperthyroid, a low dose of an antithyroid drug may be instituted. Patients need to be evaluated carefully by their physician and a discussion of the pros and cons of the various management options is required for each individual patient.

I am pregnant and have thyroid disease. Will my baby also have thyroid problems?

The answer depends on the type of thyroid disease and pattern of genetic inheritance. Patients with autoimmune thyroid disease such as Graves' disease or Hashimotos thyroiditis will usually pass on a higher risk of developing these diseases to their children. Some patients also have a strong family history of enlarged thyroid glands or multinodular goiters that may also be passed on in subsequent generations. In contrast, most forms of thyroid cancer do not have a genetic basis. As the majority of thyroid disease are treatable with good outcomes, this should not be a major source of anxiety for most pregnant mothers.

I have thyroid disease from amiodarone and I am pregnant. Will the amiodarone affect my baby?

Amiodarone can cross the placenta, and the iodine released from amiodarone can affect thyroid function in the developing baby, as described in Transient fetal hypothyroidism due to direct fetal administration of amiodarone for drug resistant fetal tachycardia. Am J Perinatol. 2001;18(2):113-6.

I have thyroid cancer and I need to be treated with radioactive iodine, yet I want to have a baby in the future. Is there an increased risk of problems with pregnancy or the baby?

Thyroid cancer is not uncommon in young woman of child bearing age. The experience of most centers has been highly favorable with pregnancy outcomes following thyroid cancer treatment. Although ovulation and menstrual periods may be slightly abnormal in the year immediately following radioactive iodine administration, ovarian failure is extremely rare, and there does not appear to be an increased risk of congenital abnormalities in babies born to this population of women. See Prognosis for fertility and ovarian function after treatment with radioiodine for thyroid cancer. Postgrad Med J. 2002 Feb;78(916):92-3. Similarly, a retrospective analysis of women with differentiated thyroid cancer who have given birth revealed no problems with pregnancy or the health of the children, as described in Pregnancy outcome after diagnosis of differentiated thyroid carcinoma: no deleterious effect after radioactive iodine treatment. Int J Radiat Oncol Biol Phys. 2004 Jul 15;59(4):992-1000. For more information, see Radioactive Iodine.

My baby was born with hypothyroidism, and this was diagnosed and treated very quickly. Will there be a problem?

There are many studies that address long term follow-up of infants with congenital hypothyroidism. In the majority of cases intellectual development and cognitive function develops normally. For representative studies, see Newborn screening for congenital hypothyroidism, Victoria, Australia, 1977-1997. Part 2: Treatment, progress and outcome. J Pediatr Endocrinol Metab. 2001 Nov-Dec;14(9):1611-34. and Influence of severity of congenital hypothyroidism and adequacy of treatment on school achievement in young adolescents: a population-based cohort study. Acta Paediatr. 2001 Nov;90(11):1249-56. Mothers are reminded that iron, calcium, and increased amounts of soy-based products may interfere with the absorption of thyroid hormone administered to the baby, so caution needs to be maintained in how the baby is given the thyroid tablet in relationship to these other supplements. See Soy formula complicates management of congenital hypothyroidism. Arch Dis Child. 2004 Jan; 89(1): 37-40.

Premature babies sometimes have low levels of thyroid hormones-will treatment with thyroid hormone be helpful for the baby?

Several studies have been done to address this issue. The available data does not support a detectable benefit for thyroid hormone therapy in this situation. See Prophylactic postnatal thyroid hormones for prevention of morbidity and mortality in preterm infants.
Cochrane Database Syst Rev. 2007 Jan 24;1:CD005948
and Postnatal thyroid hormones for respiratory distress syndrome in preterm infants. Cochrane Database Syst Rev. 2007 Jan 24;1:CD005946 and Postnatal thyroid hormones for preterm infants with transient hypothyroxinaemia. Cochrane Database Syst Rev. 2007 Jan 24;1:CD005945.

Does hyperthyroidism affect fertility in males?

There is very little evidence to suggest problems with fertility in male hyperthyroid subjects. Nevertheless, modest but detectable abnormalities in sperm analysis can be found in young hyperthyroid male patients, predominantly changes in sperm motility, which are reversible when the hyperthyroid state is corrected. See A prospective controlled study of the impact of hyperthyroidism on reproductive function in males. J Clin Endocrinol Metab. 2002 Aug;87(8):3667-71.

I am taking drugs that affect my reproductive system. Will they affect my thyroid?

The majority of drugs taken to induce or stop ovulation do not affect the thyroid. Nevertheless, there have been a few case reports linking administration of gonadotropin-releasing hormone analogues to the development of clinical thyroid disease, as described in Possible induction of Graves' disease and painless thyroiditis by gonadotropin-releasing hormone analogues. Thyroid. 2003 Aug;13(8):815-8. For a detailed overview of the safety of specific drugs, environmental agents, and treatments, during pregnancy, see

Do I need extra iodine supplementation during pregnancy?

The iodine levels in an individual and population reflect diet, and the iodine availability in local sources of water. The majority of people (and pregnanct women) who have balanced diets do not require iodine supplementation, even when iodine levels are slightly below normal during pregnancy Moderate Iodine Deficiency Is Common in Pregnancy but Does Not Alter Maternal and Neonatal Thyroid Function Tests Front Endocrinol (Lausanne). 2020 Dec 11;11:523319.


My thyroid antibodies are positive; does this have any impact on pregnancy?

There is some evidence that difficulty with conception may be associated with the presence of thyroid antibodies, a marker of autoimmunity. Similarly, the detection of positive thyroid antibodies, irrespective of normal levels of thyroid hormone, in the first trimester in a study of pregnant women from Finland was associated with a small but significant increased risk of perinatal death, hence women with positive thyroid antibodies may wish to discuss the significance of this issue with their obstetrician or physician who is monitoring the pregnancy. See Perinatal outcome of children born to mothers with thyroid dysfunction or antibodies: a prospective population-based cohort study J Clin Endocrinol Metab. 2009 Mar;94(3):772-9. Epub 2008 Dec 23. Nevertheless, it has been more difficult to demonstrate that treatment of women who have positive antibodies with L-thyroxine meaningfully increases the success rate of subsequent attempts at pregnancy. See Levothyroxine to increase live births in euthyroid women with thyroid antibodies trying to conceive: the TABLET RCT. Southampton (UK): NIHR Journals Library; 2019 Oct.

Analysis of multiple cognitive and developmental parameters in the children (3 years old) of mothers with positive thyroid antibodies revealed modest but significant correlations in some measures of child behavior, specifically attention deficit/hperactivity with positive antibody status of the mothers. Maternal Thyroid Autoimmunity During Pregnancy and the Risk of Attention Deficit/Hyperactivity Problems in Children. The Generation R Study Thyroid. 2011 Dec 16. [Epub ahead of print].  For an overview of studies in this area see Interventions for clinical and subclinical hypothyroidism in pregnancy. Cochrane Database Syst Rev. 2010 Jul 7;7:CD007752.