My cousin is a hyperthyroid patient, last year she happily married her Prince Charming, this year she wants to upgrade to become a mother, so she has a series of questions to ask me, cousin can I get pregnant? What do I need to pay attention to when I get pregnant? Can I breastfeed after I give birth? Well, let’s get to know hyperthyroidism today. What is hyperthyroidism? Hyperthyroidism is a condition in which the thyroid gland synthesizes and releases too much thyroid hormone, causing hyper-metabolism and sympathetic excitation, resulting in palpitations, sweating, increased eating and stool intake, and weight loss. Is it possible to get pregnant with hyperthyroidism? It is possible to get pregnant with hyperthyroidism, but not at any time. The best time to consider pregnancy is after thyroid function has returned to normal. So I advised my cousin to see her doctor to have her thyroid hormone levels checked. The good news is that my cousin’s thyroid hormones are basically normal, so she is happily preparing for pregnancy. Note that patients with hyperthyroidism treated with 131 iodine need to wait at least 6 months after the end of iodine treatment before considering pregnancy. What are the medications used to treat hyperthyroidism? The main treatment for hyperthyroidism lies in blocking the synthesis of thyroid hormones. The main medications are propylthiouracil (PTU) and methimazole (MMI), both of which have risks for the mother and the fetus. It has been reported that MMI may cause skin defects or other teratogenic effects in the fetus, such as nostril atresia, esophageal atresia, tracheoesophageal basket or facial deformities, so it is recommended to discontinue MMI before planning pregnancy and switch to PTU. Anti-thyroxine therapy is still needed in mid- and late pregnancy, and our guidelines recommend switching to MMI because PTU may cause liver damage. Antithyroxine drugs can cross the placental barrier. To avoid adverse effects on the fetus. The minimal dose of the drug should be used to achieve its control goal, i.e., a maternal serum FT4 value close to or mildly above the upper reference value. Note that radioactive iodine therapy is contraindicated during pregnancy because iodine can be absorbed by the fetal thyroid and can destroy the developing fetal thyroid. Some mothers-to-be are worried about the effect of anti-thyroid medication on the fetus, so they stop taking it without permission. Discontinuing the medication may lead to worsening of hyperthyroidism, which may have adverse effects on both the pregnant woman and the fetus. What are the effects of hyperthyroidism on the pregnancy and the fetus? Mild or treatable hyperthyroidism usually has little effect on pregnancy. In severe or uncontrollable hyperthyroidism, excessive secretion of thyroid hormones can inhibit the pituitary gland from secreting gonadotropins, which can easily cause miscarriage and premature birth. Hyperthyroidism in patients with hyperthyroidism does not provide adequate nutrition for the fetus, causing hypothyroidism and goiter in the fetus. Can hyperthyroidism patients breastfeed normally? Anti-thyroid medications should be taken after breastfeeding, preferably 4 hours after taking the medication. Chinese guidelines recommend that MMI is preferred, and a dose of 20-30 mg/d is safe. PTU is also safe as a second-line drug at 300 mg/d. The US guidelines recommend that MMI (maximum dose 20 mg/d) and PTU (maximum dose 450 mg/d) can be used during lactation, and the lowest effective dose is recommended considering that a small amount of PTU and MMI can enter into breast milk. The Chinese Journal of Obstetrics and Gynecology also mentions that taking PTU does not affect breastfeeding and that only a very small amount of the drug enters breast milk. Only 0.07% of PTU taken by breastfeeding mothers can be secreted by breast milk, compared to 0.5% for methimazole. Therefore, breastfeeding is considered safe for those taking PTU (<300 mg/d) and MMI (<20 mg/d). In conclusion, pregnancy and breastfeeding are possible in patients with hyperthyroidism, but it is best to consider pregnancy after thyroid function has returned to normal. Propylthiouracil is preferred as the antithyroid drug in early pregnancy, and only a small amount of PTU and MMI can enter breast milk. It is recommended to take the drug after breastfeeding.