Thyroid cancer is one of the common malignancies in women of childbearing age. What should I do if pregnancy and thyroid cancer meet unexpectedly? To answer this question, there are two aspects to consider. One is the effect of pregnancy on thyroid cancer, and the other is the effect of thyroid cancer on pregnancy. First, let’s understand the effect of pregnancy on thyroid cancer. This question can be divided into the following questions to answer. 1. Does pregnancy increase the incidence of thyroid cancer? During pregnancy, a series of physiological changes will occur in women’s body. During pregnancy, a series of physiological changes occur in the body, such as a significant increase in the level of estrogen and human chorionic gonadotropin, and the formation of maternal “immune immunity”. Can this condition lead to the development of thyroid cancer? The study concluded that pregnancy is not a risk factor for increased thyroid cancer development unless there are multiple pregnancies. 2. Does pregnancy affect the growth and malignancy of thyroid nodules? More research is needed on the changes of nodule size, number, benign and malignant ratio during pregnancy. 3. Does pregnancy accelerate the progression of thyroid cancer? This question can be discussed in three different periods and states: (1) Thyroid cancer has been diagnosed and treated before pregnancy. A case-control study in 2013 showed that in patients who were treated and in disease-free survival before pregnancy, pregnancy itself did not cause progression or recurrence of the disease. There was no significant difference in the rate of disease recurrence in patients with thyroid cancer who survived treatment disease-free, with or without pregnancy. (2) Thyroid cancer diagnosed before pregnancy and not yet treated Women who are known to have thyroid cancer before pregnancy and still proceed to pregnancy are rare and difficult to study. There is only one report from Japan, which concluded that pregnancy may cause the growth of untreated microscopic papillary thyroid cancer (MPTC). (3) Thyroid cancer is diagnosed during pregnancy. There are two different opinions: one is that there is no effect on the long-term prognosis of women with PTC diagnosed during pregnancy and those not diagnosed during pregnancy, and the other is that there is an effect, with a significantly higher proportion of persistent or recurrent thyroid cancer lesions. 4. Does pregnancy affect the treatment options for thyroid cancer? Currently, the following three treatments are commonly used for thyroid cancer: surgery, iodine 131 therapy and endocrine therapy. (1) Surgery: Surgery is one of the most important treatments for thyroid cancer. Surgery within 3 months of pregnancy, anesthesia may affect fetal organ formation and cause spontaneous abortion. Surgery in the 7th to 9th month of pregnancy is prone to preterm delivery. In contrast, surgery in the 4th to 6th month of pregnancy is rare for both maternal and fetal complications. Surgery at this stage may be an option if the thyroid cancer patient’s disease progresses (note: caution should be exercised). If monitoring during pregnancy does not reveal any significant tumor progression, postpartum surgery is the better choice to take into account the mother and fetus. (2) Iodine 131 therapy: Pregnancy is an absolute contraindication to iodine 131 therapy. (3) TSH suppression therapy TSH suppression therapy can still be performed during pregnancy. L-T4 (eugenol) is consistent with physiologically synthesized T4 and is safe for both mother and fetus. During pregnancy (especially before 20 weeks) maternal T4 is the source of all or an important supplement to the thyroid hormone needed for fetal development, and the dose of LT4 taken with TSH suppression therapy is increased by an average of 9%-26%. The target for TSH suppression is 0.1-1.5 mU/L, which is slightly higher than the level during non-pregnancy. After understanding the effect of pregnancy on thyroid cancer, let’s look at what effect thyroid cancer has on pregnancy. There are two specific questions. 1. Does thyroid cancer reduce pregnancy rates? In a large population-based matched cohort study, women of childbearing age with thyroid cancer did not have lower pregnancy rates compared to those of healthy childbearing age. 2. Do RAI (radioactive iodine) and TSH suppressive treatments for thyroid cancer affect pregnancy and offspring? Several studies have examined the effects of RAI, an important treatment for thyroid cancer, on pregnancy and offspring. Overall, there are no long-term effects of RAI treatment on gonadal function, infertility, miscarriage, fetal arrest, neonatal mortality or congenital defects. There is no increase in the incidence of thyroid cancer or other malignancies in offspring. It is safe for subsequent pregnancies and offspring. In contrast, abnormal thyroid function (except for subclinical hyperthyroidism) during surgery, RAI and TSH suppression therapy may affect pregnancy and offspring. A typical case of thyroid cancer in pregnancy A young woman with a right thyroid nodule for 2 years. 1.5 years ago, ultrasonography revealed a hypoechoic right lobe of the thyroid gland, 0.7*0.4*0.4 cm in size, with irregular morphology and multiple punctate strong echogenicity with rich blood flow. Ultrasound diagnosis: risk of thyroid cancer and surgery was recommended. Almost simultaneously, the patient was found to be prematurely pregnant. The management strategy for this case was to continue the pregnancy without puncture and other tests, with close observation and regular review. The result: a healthy baby was delivered normally at full term. Six months later, radical thyroid cancer surgery was performed, with right thyroid lobe resection and lymph node dissection in the right central region. Pathological diagnosis: papillary carcinoma of 0.5 cm in diameter size in the right lobe of the thyroid, 0.1 cm in size in the isthmus, and 0/2 lymph nodes without metastasis. TNM stage T1aN0M0. The surgery and postoperative recovery went well, and the present condition is good.