The American College of Physicians’ Guideline Grading System

Figure 1. Testing For Thyroid Dysfunction In Pregnancy

Screening for Thyroid Dysfunction Before or During Pregnancy

• All pregnant women should be verbally screened at the initial prenatal visit for any history of thyroid dysfunction, and prior or current use of either thyroid hormone (LT4) or anti-thyroid medications (methimazole [MMI], carbimazole [CM], or propylthiouracil [PTU]). (S-H)
• Universal screening to detect low free thyroxine concentrations in pregnant women is NOT recommended. (W-M)
• All patients seeking pregnancy, or newly pregnant, should undergo clinical evaluation. If any of the following risk factors are identified, testing for serum TSH is recommended. (S-M)
  1. A history of hypothyroidism/hyperthyroidism or current symptoms/signs of thyroid dysfunction
  2. Known thyroid antibody positivity or presence of a goiter
  3. History of head or neck radiation or prior thyroid surgery
  4. Age >30 years
  5. Type 1 diabetes or other autoimmune disorders
  6. History of pregnancy loss, preterm delivery, or infertility
  7. Multiple prior pregnancies (≥2)
  8. Family history of autoimmune thyroid disease or thyroid dysfunction
  9. Morbid obesity (BMI ≥40 kg/m2)
  10. Use of amiodarone or lithium, or recent administration of iodinated
      radiologic contrast
  11. Residing in an area of known moderate to severe iodine insufficiency
• There is insufficient evidence to recommend for or against universal screening for abnormal TSH concentrations in early pregnancy. (I)
• There is insufficient evidence to recommend for or against universal screening for abnormal TSH concentrations preconception, with the exception of women planning assisted reproduction or those known to have positive TPOAb. (I)

Thyroid Function Testing and Pregnancy

• When possible, population-based trimester-specific reference ranges for serum thyroid-stimulating hormone (TSH) should be defined through assessment of local population data representative of a healthcare provider’s practice. Reference range determinations should only include pregnant women with no known thyroid disease, optimal iodine intake, and negative autoantibodies to thyroid peroxidase (TPOAb) status. (S-M)
• The accuracy of serum Free T4 measurement by the indirect analog immunoassays is influenced by pregnancy and also varies significantly by manufacturer. If measured in pregnant women, assay method-specific and trimester-specific pregnancy reference ranges should be applied. (S-M)
• In lieu of measuring free T4, total T4 measurement (with a pregnancy-adjusted reference range), is a highly reliable means of estimating hormone concentration during the last part of pregnancy. Accurate estimation of the free T4 concentrations can also be done by calculating a free thyroxine index. (S-M)
  • A total T4 upper range determination can be calculated by shifting the nonpregnant limit 50% higher. However, this can only be used after week 16 of pregnancy. If a T4 measurement is required before that time (i.e. weeks 7–16 of pregnancy), a calculation can be made for the upper reference range based on increasing the non-pregnant upper reference limit by 5% per week, beginning with week 7. For example, at 11 weeks of gestation (4 weeks beyond week 7), the upper reference range for T4 is increased by 20% (four weeks × 5%/week)

Iodine Status and Nutrition

• Median urinary iodine concentrations can be used to assess the iodine status of populations, but single spot or 24-hour urine iodine concentrations are NOT valid markers for the iodine nutritional status of individual patients. (S-H)
• All pregnant women should ingest approximately 250 μg iodine daily. To achieve a total of 250 μg iodine ingestion daily, strategies may need to be varied based on country of origin. (S-H)
• In most regions, including the United States, women who are planning pregnancy or currently pregnant should supplement their diet with a daily oral supplement that contains 150 μg of iodine in the form of potassium iodide. This is optimally started 3 months in advance of planned pregnancy. (S-M)
• In low-resource countries and regions where neither salt iodization nor daily iodine supplements are feasible, a single annual dose of ~400 mg
  iodized oil for pregnant women and women of childbearing age can be used as a temporary measure to protect vulnerable populations. This should NOT be employed as a long-term strategy or in regions where other options are available. (W-M).
• There is no need to initiate iodine supplementation in pregnant women who are being treated for hyperthyroidism or who are taking levothyroxine (LT4). (W-L)
• Excessive doses of iodine exposure during pregnancy should be avoided except in preparation for the surgical treatment of Graves' disease. Clinicians should carefully weigh the risks and benefits when ordering medications or diagnostic tests that will result in high iodine exposure. (S-M)
• Sustained iodine intake from diet and dietary supplements exceeding 500 μg daily should be avoided during pregnancy due to concerns about the potential for fetal thyroid dysfunction. (S-M)

Thyroid Auto-Antibodies & Pregnancy Complications

• Euthyroid, but thyroid peroxidase (TPO) or thyroglobulin (Tg) antibody positive, pregnant women should have measurement of serum TSH concentration performed at time of pregnancy confirmation, and every 4 weeks through mid-pregnancy. (S-H)
• Selenium supplementation is NOT recommended for the treatment of TPOAb-positive women during pregnancy. (W-M)
• Intravenous immunoglobulin treatment of euthyroid women with a history of recurrent pregnancy loss is NOT recommended. (W-L)
• There is insufficient evidence to conclusively determine whether LT4 therapy decreases pregnancy loss risk in TPOAb-positive, euthyroid women who are newly pregnant. However, administration of LT4 to TPOAb-positive, euthyroid pregnant women with a prior history of loss may be considered given its potential benefits in comparison to its minimal risk. In such cases, 25–50 mcg of LT4 is a typical starting dose. (W-L)
• There is insufficient evidence to recommend for or against treating euthyroid, thyroid autoantibody positive pregnant women with LT4 to prevent preterm delivery. (I)

The Impact of Thyroid Illness upon Infertility and Assisted Reproduction

• Evaluation of serum TSH concentration is recommended for all women seeking care for infertility. (W-M)
• LT4 treatment is recommended for infertile women with overt hypothyroidism who desire pregnancy. (S-M)
• There is insufficient evidence to determine if LT4 therapy improves fertility in subclinically hypothyroid, thyroid auto-antibody negative women who are attempting natural conception (not undergoing antiretroviral therapy [ART]). However, administration of LT4 may be considered in this setting given its ability to prevent progression to more significant hypothyroidism once pregnancy is achieved. Furthermore, low dose LT4 therapy (25–50 mcg daily) carries minimal risk. (W-L)
• There is insufficient evidence to determine if LT4 therapy improves fertility in nonpregnant, euthyroid, thyroid autoantibody positive women who are attempting natural conception (not undergoing ART). Therefore, no recommendation can be made for LT4 therapy in this setting. (I)
• Subclinically hypothyroid women undergoing in vitro fertilization or intracytoplasmic sperm injection should be treated with LT4. The goal of treatment is to achieve a TSH concentration <2.5 mU/L. (S-M)
• There is insufficient evidence to determine whether LT4 therapy improves the success of pregnancy following ART in TPOAb-positive, euthyroid women. However, administration of LT4 to TPOAb-positive, euthyroid women undergoing ART may be considered given its potential benefits in comparison to its minimal risk. In such cases, 25–50 mcg of LT4 is a typical starting dose. (W-L)
• Glucocorticoid therapy is NOT recommended for euthyroid, thyroid auto-antibody positive women undergoing ART. (W-M)
• When possible, thyroid function testing should be performed either before or 1–2 weeks after controlled ovarian hyperstimulation, since results obtained during the course of controlled ovarian stimulation may be difficult to interpret. (W-M)
• In women who achieve pregnancy following controlled ovarian hyperstimulation, TSH elevations should be treated according to the recommendations outlined under Hypothyroidism and Pregnancy. In non-pregnant women with mild TSH elevations following controlled ovarian stimulation, serum TSH measurements should be repeated in 2–4 weeks, since levels may normalize. (W-M)

Hypothyroidism and Pregnancy

• In the setting of pregnancy, maternal hypothyroidism is defined as a TSH concentration elevated beyond the upper limit of the pregnancy-specific reference range. (S-H)
• The pregnancy-specific TSH reference range should be defined as follows:
  • When available, population and trimester-specific reference ranges for serum TSH during pregnancy should be defined by a provider’s institute / laboratory, and should represent the typical population for whom care is provided. Reference ranges should be defined in healthy, TPOAb-negative pregnant women with optimal iodine intake and without thyroid illness. (S-H)
  • When this is not feasible, pregnancy-specific TSH reference ranges obtained from similar patient populations, and performed using similar TSH assays should be substituted. (S-H)
  • If internal or transferable pregnancy-specific TSH reference ranges are not available, an upper reference limit of ~4.0 mU/l may be used. For most assays,
    this represents a reduction in the non-pregnant TSH upper reference limit of
    ~0.5 mU/L. (S-M)
• Treatment of overt hypothyroidism is recommended during pregnancy. (S-M)
• Pregnant women with TSH concentrations >2.5 mU/L should be evaluated for TPOAb status.
• Subclinical hypothyroidism in pregnancy should be approached as follows:
  1. LT4 therapy is recommended for:
     • TPOAb-positive women with a TSH greater than the pregnancy specific reference range (See Thyroid Function Testing and Pregnancy Section) (S-M)
     • TPOAb-negative women with a TSH >10.0 mU/L. (S-L)
  2. LT4 therapy may be considered for:
     • TPOAb-positive women with TSH concentrations >2.5 mU/L and below the upper limit of the pregnancy specific reference range. (W-M)
     • TPOAb-negative women TPO antibody negative women with TSH concentrations greater than the pregnancy specific reference range and below 10.0 mU/L. (W-L)
  3. LT4 therapy is NOT recommended for:
     • TPOAb-negative women with a normal TSH (TSH within the pregnancy specific reference range, or <4.0 mU/L if unavailable). (S-H).
• Isolated hypothyroxinemia should NOT be routinely treated in pregnancy. (W-L)
• The recommended treatment of maternal hypothyroidism is administration of oral LT4. Other thyroid preparations such as T3 or desiccated thyroid should NOT be used in pregnancy. (S-L)
• In parallel to the treatment of hypothyroidism in a general population, it is reasonable to target a TSH in the lower half of the trimester specific reference range. When this is not available, it is reasonable to target maternal TSH concentrations <2.5 mU/L. (W-M)
• Women with overt and subclinical hypothyroidism (treated or untreated), or those at risk for hypothyroidism (e.g. patients who are euthyroid but TPO or TGAb positive, posthemithyroidectomy, or treated with radioactive iodine) should be monitored with a serum TSH measurement approximately every 4 weeks until mid-gestation, and at least once near 30 weeks gestation. (S-H)
• Treated hypothyroid women of reproductive age should be counseled regarding the likelihood of increased demand for LT4 during pregnancy. Such women should also be counseled to contact their caregiver immediately upon a confirmed or suspected pregnancy. (S-H)
• In hypothyroid women treated with LT4 who are planning pregnancy, serum TSH should be evaluated preconception, and LT4 dose
  adjusted to achieve a TSH value between the lower reference limit
  and 2.5 mU/L. (S-M)
• Following delivery, LT4 should be reduced to the patient’s preconception dose. Additional thyroid function testing should be performed at approximately 6 weeks postpartum. (S-M)
• Some women in whom LT4 is initiated during pregnancy may not require LT4 postpartum. Such women are candidates for discontinuing LT4, especially when the LT4 dose is ≤50 mcg daily. The decision to discontinue LT4, if desired, should be made by the patient and their caregiver. If LT4 is discontinued, serum TSH should be evaluated in
  ~6 weeks. (W-M)
• In the care of women with adequately treated hypothyroidism, no other maternal or fetal testing (such as serial fetal ultrasounds, antenatal testing, and/or umbilical blood sampling) is recommended beyond measurement of maternal thyroid function unless needed due to other circumstances of pregnancy. An exception to this is women with Graves’ disease effectively treated with 131I ablation or surgical resection, who require thyrotropin receptor antibodies (TRAb) monitoring. (S-M)

Thyrotoxicosis in Pregnancy

• When a suppressed serum TSH is detected in the first trimester (TSH less than the reference range), a medical history, physical examination, and measurement of maternal serum Free T4 or total T4 concentrations should be performed. Measurement of TSH receptor antibodies (TRAb), and maternal total T3, may prove helpful in clarifying the etiology of thyrotoxicosis. (S-M)
• Radionuclide scintigraphy or radioiodine uptake determination should NOT be performed in pregnancy. (S-H)
• The appropriate management of abnormal maternal thyroid tests attributable to gestational transient thyrotoxicosis and/or hyperemesis gravidarum includes supportive therapy, management of dehydration, and hospitalization if needed. Antithyroid drugs are NOT recommended, though beta-blockers may be considered. (S-M)
• In all women of childbearing age who are thyrotoxic, the possibility of future pregnancy should be discussed. Women with Graves’ disease seeking future pregnancy should be counseled regarding the complexity of disease management during future gestation, including the association of birth defects with antithyroid drug use. Preconception counseling should review the risks and benefits of all treatment options, and the patient’s desired timeline to conception. (S-H)
• Thyrotoxic women should be rendered stably euthyroid before attempting pregnancy. Several treatment options exist, each of which are associated with risks and benefits. These include 131I ablation, surgical thyroidectomy, or anti-thyroid drug (ATD) therapy. (S-M)
• Women taking methimazole (MMI) or propylthiouracil (PTU) should be instructed to confirm potential pregnancy as soon as possible. If the pregnancy test is positive, pregnant women should contact their caregiver immediately. (S-H)
• New Pregnancy
  1. In a newly-pregnant woman with Graves’ disease, who is euthyroid on a low dose of MMI (≤5–10 mg/day) or PTU (≤100–200 mg/day), the physician should consider discontinuing all antithyroid medication given potential teratogenic effects. The decision to stop medication should take into account the disease history, goiter size, duration of therapy, results of recent thyroid function tests, TRAb measurement, and other clinical factors. (W-L)
  2. Following cessation of antithyroid medication, maternal thyroid function testing (TSH, and FT4 or total T4 [TT4]) and clinical examination should be performed every 1–2 weeks to assess maternal and fetal thyroid status. If the pregnant woman remains clinically and biochemically euthyroid, test intervals may be extended to 2-4 weeks during the 2nd and 3rd trimester. (W-L)
  3. At each assessment, the decision to continue conservative management (withholding antithyroid medication) should be guided both by the clinical and the biochemical assessment of maternal thyroid status. (W-L)
• High Risk
  • In pregnant women with a high risk of developing thyrotoxicosis if antithyroid drugs were to be discontinued, continued antithyroid medication may be necessary. Factors predicting high clinical risk include being currently hyperthyroid, or requirement of 5–10 mg/day MMI or 100–200 mg/day PTU to maintain a euthyroid state. In such cases:
  • PTU is recommended for the treatment of maternal hyperthyroidism through 16 weeks of pregnancy. (S-M)
  • Pregnant women receiving MMI who are in need of continuing therapy during pregnancy should be switched to PTU as early as possible. (W-L)
  • When shifting from MMI to PTU, a dose ratio of approximately 1:20 should be used (e.g. MMI 5 mg daily = PTU 100 mg twice daily). (S-M)
  • If ATD therapy is required after 16 weeks gestation, it remains unclear whether PTU should be continued or therapy changed to MMI. Since both medications are associated with potential adverse effects and shifting potentially may lead to a period of less-tight control, no recommendation regarding switching antithyroid drug medication can be made at this time. (I)
• Antithyroid Drugs
  • In women being treated with antithyroid drugs in pregnancy, FT4/TT4 and TSH should be monitored approximately every 4 weeks. (S-M)
  • Antithyroid medication during pregnancy should be administered at the lowest effective dose of MMI or PTU, targeting maternal serum FT4/TT4 at or moderately above the reference range. (S-H)
• A combination regimen of LT4 and an antithyroid drug should NOT be used in pregnancy, except in the rare situation of isolated fetal hyperthyroidism. (S-H)
• Thyroidectomy in pregnancy may be indicated for unique scenarios. If required, the optimal time for thyroidectomy is in the second trimester of pregnancy. If maternal TRAb concentration is high (>3x upper reference for the assay) the fetus should be carefully monitored for development of fetal hyperthyroidism throughout pregnancy, even if the mother is euthyroid post-thyroidectomy. (S-H)
• We concur with the American College of Obstetricians and Gynecologists' Committee on Obstetric Practice consensus guidelines (written in 2011 and revised in 2015) which state the following:
  1. "A pregnant woman should never be denied indicated surgery, regardless of trimester.
  2. Elective surgery should be postponed until after delivery.
  3. If possible, nonurgent surgery should be performed in the second trimester when preterm contractions and spontaneous abortion are least likely.”
     • In the setting of a patient with Graves’ Disease undergoing urgent, non-thyroid surgery, if the patient is well controlled on ATD, no other preparation is needed. Beta-blockade should also be utilized if needed. (S-M)
• TRAb Measurement
  1. If the patient has a past history of Graves’ disease treated with ablation (radioiodine or surgery), a maternal serum determination of TRAb is recommended at initial thyroid function testing during early pregnancy. (S-M)
  2. If maternal TRAb concentration is elevated in early pregnancy, repeat testing should occur at weeks 18–22. (S-M)
  3. If maternal TRAb is undetectable or low in early pregnancy, no further TRAb testing is needed. (W-M)
  4. If a patient is taking ATDs for treatment of Graves’ hyperthyroidism when pregnancy is confirmed, a maternal serum determination of TRAb is recommended. (W-M)
  5. If the patient requires treatment with ATDs for Graves’ disease through mid pregnancy, a repeat determination of TRAb is again recommended at weeks 18–22. (S-M)
  6. If elevated TRAb is detected at weeks 18–22 or the mother is taking ATD in the third trimester, a TRAb measurement should again be performed in late pregnancy (weeks 30–34) to evaluate the need for neonatal and postnatal monitoring. (S-H)
• Fetal surveillance should be performed in women who have uncontrolled hyperthyroidism in the second half of pregnancy, and in women with high TRAb levels detected at any time during pregnancy (>3x the upper limit of normal). A consultation with an experienced obstetrician or maternal-fetal medicine specialist is recommended. Monitoring may include ultrasound to assess heart rate, growth, amniotic fluid volume, and the presence of fetal goiter. (S-M)
• Cordocentesis should be used in rare circumstances and performed in an appropriate setting. It may occasionally be of use when fetal goiter is detected in women taking antithyroid drugs to help determine whether the fetus is hyperthyroid or hypothyroid. (W-L)
• If ATD therapy is given for hyperthyroidism caused by autonomous nodules, the fetus should be carefully monitored for goiter and signs of hypothyroidism during the 2nd half of pregnancy. A low dose of ATD should be administered with the goal of maternal FT4 or TT4 concentration at or moderately above the reference range. (S-L)

Thyroid Nodules and Thyroid Cancer During Pregnancy

• For women with suppressed serum TSH levels that persist beyond 16 weeks gestation, FNA of a clinically relevant thyroid nodule may be deferred until after pregnancy. At that time, if serum TSH remains suppressed, a radionuclide scan to evaluate nodule function can be performed if not breastfeeding. (S-L)
• The utility of measuring calcitonin in pregnant women with thyroid nodules is unknown. The task force cannot recommend for or against routine measurement of serum calcitonin in pregnant women with thyroid nodules. (I)
• Thyroid nodule FNA is generally recommended for newly detected nodules in pregnant women with a non-suppressed TSH. Determination of which nodules require FNA should be based upon the nodule’s sonographic pattern as outlined in Table 2. The timing of FNA, whether during gestation or early postpartum, may be influenced by the clinical assessment of cancer risk, or by patient preference. (S-M)
• Radionuclide scintigraphy or radioiodine uptake determination should NOT be performed during pregnancy. (S-H)
• Pregnant women with cytologically benign thyroid nodules do not require special surveillance strategies during pregnancy and should be managed according to the 2015 ATA Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4739132/). (S-M)
• Pregnant women with cytologically indeterminate (AUS/FLUS, SFN, or SUSP) nodules, in the absence of cytologically malignant lymph nodes or other signs of metastatic disease, do not routinely require surgery while pregnant. (S-M)
• During pregnancy, if there is clinical suspicion of an aggressive behavior in cytologically indeterminate nodules, surgery may be considered. (W-L)
• Molecular testing is NOT recommended for evaluation of cytologically indeterminate nodules during pregnancy. (S-L)
• Papillary thyroid carcinoma (PTC) detected in early pregnancy should be monitored sonographically. If it grows substantially before 24–26 weeks gestation, or if cytologically malignant cervical lymph nodes are present, surgery should be considered during pregnancy. However, if the disease remains stable by midgestation, or if it is diagnosed in the second half of pregnancy, surgery may be deferred until after delivery. (W-L)
• The impact of pregnancy on women with newly diagnosed medullary carcinoma or anaplastic cancer is unknown. However, a delay in treatment is likely to adversely impact outcome. Therefore, surgery should be strongly considered, following assessment of all clinical factors. (S-L)
• Pregnant women with thyroid cancer should be managed at the same TSH goal as determined pre-conception. TSH should be monitored approximately every 4 weeks until 16–20 weeks of gestation, and at least once between 26–32 weeks of gestation. (S-M)
• Pregnancy should be deferred for 6 months after a woman has received therapeutic radioactive iodine (131I) treatment. (S-L)
• Ultrasound and thyroglobulin monitoring during pregnancy is not required in women with a history of previously treated differentiated thyroid carcinoma with undetectable serum thyroglobulin levels (in the absence of Tg autoantibodies) classified as having no biochemical or structural evidence of disease prior to pregnancy. (S-M)
• Ultrasound and thyroglobulin monitoring should be performed during pregnancy in women diagnosed with well-differentiated thyroid cancer and a biochemically or structurally incomplete response to therapy, or in patients known to have active recurrent or residual disease. (S-M)
• Ultrasound monitoring of the maternal thyroid should be performed each trimester during pregnancy in women diagnosed with papillary thyroid microcarcinoma (PTMC) who are under active surveillance. (W-L)

Postpartum Thyroiditis (PPT)

• All patients with depression, including postpartum depression, should be screened for thyroid dysfunction. (S-L)
• During the thyrotoxic phase of PPT, symptomatic women may be treated with beta-blockers. A beta-blocker which is safe for lactating women, such as propranolol or metoprolol, at the lowest possible dose to alleviate symptoms, is the treatment of choice. Therapy is typically required for a few weeks. (S-M)
• Antithyroid drugs are NOT recommended for the treatment of the thyrotoxic phase of PPT. (S-H)
• Following the resolution of the thyrotoxic phase of PPT, serum TSH should be measured in approximately 4–8 weeks (or if new symptoms develop) to screen for the hypothyroid phase. (S-H)
• LT4 should be considered for women with symptomatic hypothyroidism due to PPT. If treatment is not initiated, their TSH level should be repeated every 4–8 weeks until thyroid function normalizes. LT4 should also be started in hypothyroid women who are attempting pregnancy or who are breastfeeding. (W-M)
• If LT4 is initiated for PPT, discontinuation of therapy should be attempted after 12 months. Tapering of LT4 should be avoided when a woman is actively attempting pregnancy or is pregnant. (W-L)
• Women with a prior history of PPT should have TSH testing annually to evaluate for the development of permanent hypothyroidism. (S-H)
• Treatment of euthyroid thyroid antibody-positive pregnant woman with either LT4 or iodine to prevent PPT is ineffective and is NOT recommended. (S-H)
• A history of maternal thyroid illness, use of antithyroid medications (PTU, MMI) during gestation, or measurements of abnormal maternal thyroid function or TRAb during gestation should be communicated to the newborn’s neonatologist or pediatrician. (S-M)
• The severity of maternal and fetal thyroid illness should guide the timing of communication. Severe, progressive, or complex thyroid illness during pregnancy mandates communication with the neonatologist or pediatrician before birth and consideration of consultation with a pediatric endocrinologist. Most other illness is optimally communicated shortly after birth. (S-M)
• All newborns should be screened for hypothyroidism by blood spot analysis typically 2–4 days after birth. (S-H)

Thyroid Disease and Lactation

• As maternal hypothyroidism can adversely impact lactation, women experiencing poor lactation without other identified causes should have TSH measured to assess for thyroid dysfunction. (W-L)
• Given its adverse impact upon milk production and letdown, subclinical and overt hypothyroidism should be treated in lactating women seeking to breastfeed. (W-L)
• The impact of maternal hyperthyroidism upon lactation is not well understood. Therefore, no recommendation to treat maternal hyperthyroidism on the grounds of improving lactation can be made
  at this time. (I)
• The use of 131I is contraindicated during lactation. If required, 123I can be used if breast milk is pumped and discarded for 3–4 days before breastfeeding is resumed. Similarly, Tc-99m pertechnetate administration requires breast milk to be pumped and discarded during the day of testing. (S-M)
• Excepting treatment decisions specifically made on the grounds of improving lactation (discussed above), the decision to treat hyperthyroidism in lactating women should be guided by the same principles applied to non-lactating women. (S-L)
• When antithyroid medication is indicated for women who are lactating, both MMI (up to maximal dose of 20 mg daily) and PTU (up to maximal dose of 450 mg daily) can be administered. Given a small, but detectable amount of both PTU and MMI transferred into breast milk, the lowest effective does of MMI/carbimazole (CM) or PTU should always be administered. (S-M)
• Breastfed children of women who are treated with antithyroid drugs should be monitored for appropriate growth and development during routine pediatric health and wellness evaluations. Routine assessment of serum thyroid function in the child is NOT recommended. (W-M)
• All breastfeeding women should ingest approximately 250 mcg of dietary iodine daily. (S-H)
• Breastfeeding women should supplement their diet with a daily oral supplement that contains 150 mcg of iodine. This is optimally delivered in the form of potassium iodide (present in a multivitamin) because kelp and other forms of seaweed do not provide a consistent delivery of daily iodine. (S-M)
• In severely iodine deficient, low-resource regions, where universal salt iodization is lacking and daily supplementation is not feasible, lactating women should receive one dose of 400 mg iodine as oral iodized oil soon after delivery. (S-H)
• As is the case during pregnancy, sustained iodine intake while breastfeeding that exceeds 500–1100 mcg daily should be avoided
  due to concerns about the potential for inducing hypothyroidism in
  the infant. (S-M)