Is it possible to lose fertility after thyroidectomy?

Dear Ask The Doctor: Hello Dr. I have a Medullary thyroid cancer and my gland take-out before 18 months and I take 175 gm thyroxin hormone daily. Now, I am worried about my fertility. I have 6 years and 6 months child. Besides, after three months of surgery, my wife gets pregnancy and by chance during delivery the child died. Now, we are excited to have a child and we tried three times but my wife could not get pregnancy. So, is there any relation with my case possible loss my fertility? If there is a chance of loss, what shall I do to have a child? What kind of treatment is important to maintain my fertility status?

Total thyroidectomy (total removal of the thyroid gland) can potentially cause hypothyroidism (hypoactive thyroid or low thyroid hormones). Thyroxine will replace the absence of thyroid hormone production once the thyroid gland is removed. The thyroid hormones are also necessary to produce reproductive hormones (e.g. testosterone). In hypothyroidism, men may have low sex drive, some may have infertility issues because of low reproductive hormones, as an effect of low thyroid hormones. But if you are taking Levothyroxine, your blood thyroid hormone levels should be in the normal range and there is little need to worry regarding infertility. This will be enough to replace the anticipated absence or lack of thyroid hormones after thyroidectomy. In other words, it will remotely affect your fertility, if at all. The mere fact you and your wife still conceived after the surgery is enough proof that your fertility status is okay. The age of your wife will also matter. Once a woman reaches 35 or 36, it is harder to conceive as compared to women in their 20s. I also suggest take note of the menstrual cycle of your wife. If she has a 28 day menstrual cycle (period comes almost at the same time every month), then you should have sex during the time she is very fertile. Day 1 of the menstrual cycle is first day of the period; for women with a regular (28-day) cycle, having sex on Day 10 to Day 20 will have higher chances of getting pregnant, the highest chances will be on Day 13-15. Also, bear in mind that it will take 2 days for the testicles to regenerate sperm cells so it is better to have sex every other day, not every day.  I do hope I have appeased your concerns. Take care always.