Why thyroid test in pregnancy

Clinicians have debated the concept of universal thyroid testing in pregnant women for quite some time now. While it may help to lower complications and protect fetal brain development, others say it could lead to overdiagnosis among other risks. A recent analysis published in F r ontiers in Endocrinology presents the pros and cons of universal testing. The authors note that optimal thyroid hormone levels have been proven to maintain pregnancy and aid in fetus development. Thyroid dysfunction is common in women of childbearing age.

It can result in substantial adverse obstetric and child neurodevelopmental outcomes. It is easy to detect via blood testing and can be corrected with inexpensive and available treatments, they say. They say that fetuses are completely reliant on maternal thyroid hormones up to 16 weeks, which is a critical time in brain development. It also raises the risk of premature birth, preeclampsia and other complications. In the United States, doctors tend only to screen women at high risk for thyroid dysfunction or those who have a history of autoimmune diseases or preterm deliveries.

Doctors tend to debate the screening based on cases when a women has no symptoms or abnormal or borderline thyroid tests. Treating borderline cases detected via a universal screening could risk patient anxiety and puts pressure on clinicians. Most noted is that evidence is lacking when it comes to the benefits of treating women with abnormal and borderline test results.

On the flip side, Taylor said that universal thyroid screening in early pregnancy could improve child IQ and reduce complications of pregnancy.

The American Thyroid Association and the Endocrine Society do not recommend universal thyroid screening for pregnant women. A statement from the American College of Obstetrics and Gynecology also does not recommend universal testing. Clin Chem. Kravets I. Hyperthyroidism: diagnosis and treatment. Am Fam Physician. Thyroiditis: an integrated approach. European Society for Paediatric Endocrinology consensus guidelines on screening, diagnosis, and management of congenital hypothyroidism.

Aquino, AC. Thyroid during pregnancy: how it changes, how to test. Thyroid disease in pregnancy. Casey B, de Veciana M. Thyroid screening in pregnancy. Am J Obstet Gynecol. Subscribe for Updates.

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ARUP will only use your email address to respond to your feedback. See the ARUP privacy policy for more information regarding email use. Leave this field blank. Quick Answers for Clinicians Who should be screened for thyroid disease in pregnancy? What is the appropriate reference interval for thyroid stimulating hormone in pregnancy? Should the free thyroxine T4 index be used in pregnancy? How can thyroid test results help distinguish patients with euthyroid sick syndrome in late pregnancy?

Which testing algorithms are related to this topic? Thyroid Disease Testing Algorithm. Indications for Testing Laboratory testing may be used to screen for and diagnose thyroid disease in women at high risk for thyroid disease who are pregnant or plan to become pregnant. Screening In general, testing is not recommended for asymptomatic women who are not at increased risk for thyroid disease ; aggressive case finding in individuals at high risk for thyroid disease may be a suitable alternative.

Laboratory Testing Recommendations for laboratory testing for thyroid disease in pregnancy vary by society. Other Tests and Procedures Radioactive iodine testing is not recommended in pregnant individuals.

Monitoring TSH measurement is the recommended initial test and should be performed as soon as possible after conception in women with overt hypothyroidism who are being treated with levothyroxine. Testing for Postpartum Thyroiditis Recommendations for postpartum thyroiditis testing vary by society. Fetal Testing In general, laboratory evaluation of fetal thyroid function is not recommended.

Preferred test for screening and monitoring thyroid function in pregnant women. Thyroid Stimulating Hormone Preferred test for thyroxine measurement in pregnant women; order following abnormal TSH result. The Endocrine Society recommends screening only pregnant women at high risk of thyroid disease using serum TSH measurement Table 3. Autoimmune disorder. High-dose neck radiation. Postpartum thyroid dysfunction.

Previous delivery of infant with thyroid disease. Therapy for hyperthyroidism. Type 1 diabetes mellitus. Information from references 2 and 3. Women with hypothyroidism should be counseled about the importance of achieving euthyroidism before conception because of the risk of decreased fertility and miscarriage.

Preconception counseling for women with known hyperthyroidism should include discussion of available treatments and potential adverse effects, as well as the impact on future pregnancies. Standard treatments include long-term antithyroid medication, radioactive iodine ablation, and near-total thyroidectomy. Potential adverse fetal effects of antithyroid medications include congenital abnormalities and neonatal hypothyroidism caused by transplacental transfer.

The incidence of hypothyroidism during pregnancy is estimated to be 0. Worldwide, the most common cause of hypothyroidism is iodine deficiency. In iodine-sufficient regions, the most common causes are autoimmune thyroiditis and iatrogenic hypothyroidism after treatment for hyperthyroidism.

Overt and subclinical hypothyroidism have been associated with adverse effects on pregnancy and fetal development Table 4. Maternal: heart failure, placental abruption, preeclampsia, preterm delivery. Fetal: goiter, intrauterine growth restriction, small for gestational age, stillbirth, thyroid dysfunction. Methimazole Tapazole : aplasia cutis, choanal or esophageal atresia.

Anemia, fetal neurocognitive deficits, gestational hypertension, low birth weight, miscarriage, placental abruption, preeclampsia, preterm birth. Levothyroxine: little to no effect on hypertensive disorders and abruption; reduces miscarriage and preterm birth, and improves fetal intellectual development. Information from references 1 through 3. Levothyroxine is the mainstay of treatment for maternal hypothyroidism Table 5. After delivery, levothyroxine should be decreased to the prepregnancy dosage over a four-week period, and further adjustment should be guided by TSH levels four to six weeks after delivery.

Methimazole Tapazole; preferred agent after first trimester , 10 to 40 mg per day orally in two divided doses. Serum free thyroxine in upper one-third of normal range 2. Measurement of serum TSH and free thyroxine every two weeks until on stable medication dosage 2 , 3. Weekly beginning at 32 to 34 weeks' gestation in women with poorly controlled hyperthyroidism; consider testing earlier or more frequently in patients with other indications for testing 3 , 14 , Levothyroxine, to mcg per day orally 2.

Measurement of serum TSH at 4 to 6 weeks' gestation, then every 4 to 6 weeks until 20 weeks' gestation and on stable medication dosage, then again at 24 to 28 weeks' and 32 to 34 weeks' gestation 2 , Typically reserved for women with coexisting conditions or obstetric indications, and in patients with other indications for testing Information from references 2 , 3 , and 14 through Information from reference Treatment seems to reduce the incidence of miscarriage and preterm birth, and to improve fetal intellectual development; however, it has little impact on hypertensive disorders and placental abruption.

Hyperthyroidism is less common than hypothyroidism, with an approximate incidence during pregnancy of 0. Clinical symptoms of hyperthyroidism include tachycardia, nervousness, tremor, sweating, heat intolerance, proximal muscle weakness, frequent bowel movements, decreased exercise tolerance, and hypertension.

Other less common causes of hyperthyroidism include gestational trophoblastic disease, nodular goiter or solitary toxic adenoma, viral thyroiditis, and tumors of the pituitary gland or ovary.

Transient hyperthyroidism may also be associated with hyperemesis gravidarum and gestational transient thyrotoxicity, most likely resulting from the stimulatory effect of human chorionic gonadotropin on the thyroid.

The natural history of hyperthyroid disorders varies with the underlying etiology. Graves disease is typically characterized by an initial exacerbation of symptoms in the first trimester, and is thought to be caused by the initial stimulatory effect of human chorionic gonadotropin on the thyroid. Symptoms usually improve during the second half of the pregnancy, only to worsen again in the postpartum period.

Overt hyperthyroidism during pregnancy is treated with methimazole Tapazole or propylthiouracil Table 5. The main concern in women with hyperthyroidism is the potential effect on the fetus. Thyroid receptor antibodies should be measured by the end of the second trimester in women with active Graves disease, a history of Graves disease treated with radioactive iodine or thyroidectomy, or a history of a previous infant with Graves disease.

The most common cause of postpartum thyroid dysfunction is postpartum thyroiditis, which affects 1. A radioactive iodine uptake scan can help distinguish postpartum thyroiditis from Graves disease, but is contraindicated in breastfeeding women. Patients must limit close contact with others for a time after the study. Differentiation of the hyperthyroid phase of postpartum thyroiditis from Graves disease is important because Graves disease requires antithyroid therapy.

In contrast, postpartum hypothyroidism should be treated with levothyroxine in women who are symptomatic or breastfeeding, or who wish to become pregnant, and may require lifetime supplementation. Women with a history of type 1 diabetes and women with thyroglobulin or thyroperoxidase autoantibodies are at increased risk of postpartum thyroiditis.

Key words were thyroid disease and pregnancy. Article selection was limited to human studies, original research, systematic reviews, and current clinical practice guidelines. Search date: August 22, Already a member or subscriber?

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Navy Medical Corps, the U. Navy, or the U. Department of Defense. Interventions for clinical and subclinical hypothyroidism in pregnancy.