Thyroid Disorders and Pregnancy Q&A Feng Zhihai, Department of Endocrinology, The First Affiliated Hospital of Henan College of Traditional Chinese Medicine Q: Why do I have an increased risk of thyroid disorders during pregnancy or childbirth? A: During pregnancy, the thyroid gland and the levels of thyroid hormones it produces change, and thyroid disorders such as hypothyroidism may occur. Iodine deficiency is also a trigger for thyroid disorders because of the increased need for iodine during pregnancy and breastfeeding. Other causes of thyroid disorders include Hashimoto’s thyroiditis, an autoimmune thyroid disorder caused by an abnormal immune system that attacks and destroys thyroid cells. Q: How often should I have my thyroid checked during my pregnancy? A: It is recommended that thyroid function be checked at least once when pregnancy is confirmed. For those who are already on treatment for thyroid disease, thyroid function should be checked every 6-8 weeks during pregnancy to ensure that the mother’s thyroid gland is functioning properly. Q: If I have thyroid disease, how will it affect my fetus? A: If thyroid disorders are not diagnosed and treated in a timely manner, they may have adverse effects on the fetus. For example, if you have hypothyroidism, it may affect the mental development of the fetus if you do not receive timely treatment. Therefore, it is very important to have your thyroid function checked regularly. Q: If I have thyroid disease, will my child have hyperthyroidism or hypothyroidism? A: If a mother has thyroid disease, about half of her offspring are likely to grow up with thyroid disease. Therefore, it is critical that both mothers with thyroid disease and their children be aware of the signs and symptoms of thyroid disease and have their thyroids checked regularly. Q: Why is iodine intake so important? A: Iodine is an important component in the synthesis of thyroid hormones, which are necessary for the proper functioning of the body. During the first 10-12 weeks of pregnancy, the fetus is completely dependent on the mother for the thyroid hormones it needs. Later, the fetus is able to synthesize thyroid hormones on its own. However, the fetus is still dependent on the mother to ensure adequate iodine levels. Q: How much iodine should I consume per day? A: Adult women should consume 150 micrograms of iodine per day. During pregnancy and breastfeeding, iodine intake should be increased to 250 mcg/day. Q: Do I need to continue to have my thyroid checked after delivery? A: Approximately 7% of women develop abnormal thyroid function within 1 year after delivery, known as postpartum thyroiditis (PPT), so new mothers should be aware of this condition and have their thyroid checked when symptoms of the condition appear. Q: How can I determine my thyroid function after pregnancy? A: TSH 0.1-2.5 in early pregnancy (1-12 weeks), 0.2-3.0 in mid pregnancy (13-27 weeks), 0.3-3.0 in late pregnancy (28-40 weeks), FT3 and FT4 levels are mildly higher than non-pregnancy levels (5%-10%) around 10 weeks of gestation; as pregnancy progresses, FT3 and FT4 levels gradually decrease, and in the second trimester, the reference values are lower than non-pregnancy levels. In the second trimester, the reference values are 10%-30% lower than the non-pregnancy reference values. Serum TT4 and TT3 increase in the early stages of pregnancy. From the latter part of early pregnancy, TT3 and TT4 remain stable, and in mid- and late pregnancy, their reference range approaches 1.5 times the non-pregnancy reference value. This is due to the increase in TBG stimulated by the rise in estrogen during pregnancy. Q: How high is thyrotropin (TSH) during pregnancy that requires levothyroxine tablets? A: TSH > 2.5 mIU/L in the first trimester and > 3.0 mIU/L after trimester should be treated with levothyroxine tablets. Q: Do women with hypothyroidism, who maintain a TSH of about 3-4 before pregnancy, need to increase the dosage of Eugenol after pregnancy? A: If hypothyroidism is diagnosed before pregnancy, adjust the L-T4 dose so that TSH is <2.5 before pregnancy; depending on the value of TSH, it is usually necessary to increase the dose. Q: In what cases will termination of pregnancy be recommended if pregnancy is combined with Hashimoto? Do I need a diet with less iodine if I continue the pregnancy? A: Hashimoto does not affect pregnancy. Regular review and active prevention of hypothyroidism do not require a diet with less iodine. Q: How to determine the starting dose of LT4 for hypothyroidism in pregnancy? Are there any side effects of the medication? A: The earlier the target is reached, the better (preferably within 8 weeks of pregnancy). The starting dose of L-T4 is as follows: for pregnancy-specific reference value < TSH ≤ 8.0mIU/L, the starting dose of L-T4 is 50ug/d (1 tablet); for 8.0mIU/L < TSH ≤ 10.0mIU/L, the starting dose of L-T4 is 75ug/d (1½ tablets); for TSH > 10.0mIU/L, the starting dose of L-T4 is 100ug/d (2 tablets). There are no side effects with the right dose of medication. Q: Should I use propylthiocarbamidine or methimazole for hyperthyroidism during breastfeeding? Why? A: The use of PTU 300 mg/day or MMI 20-30 mg/day during lactation has no significant effect on the brain development of the infant, who should be monitored for thyroid function. MMI is preferred and PTU is the second-line drug due to hepatotoxicity. ATD should be given after breastfeeding and 3-4 hours apart before the next breastfeeding. Monitor fetal thyroid function. Q: What should I do if my TSH is at a critical level in pregnancy with thyroid disease? A: Monitor dynamically and recheck every 2-4 weeks. Q: What are the indications for medication and discontinuation of hypothyroidism in pregnancy and how long is the review period? A: L-T4 is the first choice of replacement therapy, dry thyroxine tablets are not recommended. L-T4 treatment details: if hypothyroidism is diagnosed before pregnancy, adjust L-T4 dose to TSH <2.5 before pregnancy; during pregnancy, increase L-T4 dose by 25%-30% compared to non-pregnancy; during pregnancy, diagnose hypothyroidism and treat immediately; adjust L-T4 dose according to TSH. -If the L-T4 dose is adjusted, TSH should be measured every 2-4 weeks; the earlier the target is reached, the better (preferably within 8 weeks of gestation); after the TSH target is reached, TSH, FT4 and TT4 should be monitored every 4 weeks; L-T4 should be taken in the morning on an empty stomach, followed by breakfast 1 hour later. Discontinuation of medication: if hypothyroidism is diagnosed before pregnancy, continue medication after delivery; if no hypothyroidism before pregnancy and subclinical hypothyroidism is detected during pregnancy, medication can be discontinued directly after delivery. Q: How to adjust the dose of medication for hyperthyroidism in pregnancy? (1) Maximum dose of PTU 50-300 mg/day, or MMI 5-15 mg/day. (2) Check thyroid function every 2 weeks at the beginning of treatment, and then extend it to 2-4 weeks once clinical symptoms and thyroid function improve, and the dose of ATD should be halved. Maintenance therapy until 32 weeks of gestation is currently advocated to avoid recurrence. (4) In case of recurrence, treatment with ATD can be repeated. The goals of drug therapy for hyperthyroidism in pregnancy are (1) to reduce the dose of ATD as much as possible; (2) to control the symptoms as soon as possible; (3) to normalize the thyroid function as soon as possible, with serum FT4 close to or slightly above the upper limit of normal; (4) TSH level cannot be used as a monitoring indicator for hyperthyroidism treatment; (5) to ensure that the mother and the fetus are free from complications without: ATD in combination with -LT4 (blockade - replacement therapy) and L-LT4. The combination of ATD and -LT4 (blockade - replacement therapy) with L-T4 will increase the dose of ATD to control hyperthyroidism and lead to hypothyroidism in the fetus, so the combined use of L-T4 is not recommended for hyperthyroidism in pregnancy. Q: Is this type of drug contraindicated during pregnancy and lactation in hyperthyroidism? A: Use with caution. The prevalence of spontaneous abortion is 24.4% and 5.5% in normal people; long-term use may cause intrauterine growth retardation, prolonged labor, neonatal bradycardia, hypotension, neonatal hypoglycemia and other complications, so the pros and cons should be weighed and used with caution.