The Thyroid Gland is a butterfly-shaped organ in the neck that plays an important role in bodily functions. Fertility gets affected due to imbalances in thyroid gland functions. It's responsible for regulating the conception process.  If the thyroid functions normally, then it supports the hormonal changes that are required for the development of the fetus.\nThyroid dysfunction is frequently associated with female infertility. Thyroid function should be carefully monitored in both males and females, in couples seeking spontaneous pregnancy as well as IVF Treatment, as treatment is generally immediate and likely to improve chances of success. \nInfertility, defined as the inability to conceive after at least 1 year of unprotected sexual intercourse, affects about 15% of couples, and it is particularly common in developing countries. Male and female partners alone are responsible for 20–30% of cases, respectively, but contribute to 50% of cases overall.
\nThyroid and female fertility\nDuring pregnancy, the thyroid gland increases due to iodine supply. The thyroid function changes in two ways: by increase in thyroxine binding globulin (TBG) due to estradiol level, and stimulatory effects of human chorionic gonadotropin (hCG), with repercussion on the hypothalamic–pituitary–thyroid axis. Consequently, thyroid hormone impairment could affect markers of ovarian reserve, including anti-Mullerian hormone (AMH).\nThyroid hormones and hormone receptors also regulate the endometrium's receptivity, which is the stage where all the actors, including thyroid hormones, cooperate to prepare and allow the implantation window of the blastocyst, with variations during the menstrual cycle.\nImbalanced thyroid hormones and Female fertility:\nMenstrual irregularities \nAnovulation \nUnexplained infertility\nLuteal phase problems \nEarly pregnancy miscarriages\nImbalanced thyroid hormones and Male fertility:\nSemen volume and sperm motility are affected\nProblems with Erectile \nDelayed Ejaculation\nLoss of libido\nMale breast enlargement\nFor any infertile couple, thyroid hormone screening is a must. Once the underlying thyroid problems are treated with medications, and thyroid hormones return to adequate levels, many times fertility may be restored. \nHyperthyroidism and Pregnancy\nMany maternal and neonatal complications arise due to the consequences of hyperthyroidism in pregnancy. Thyrotoxicosis can lead to significant maternal complications, including miscarriage. In hypothyroidism, hormonal changes in androgens and estrogen have been observed, following lower metabolic clearance of androstenedione and estrone, and a higher rate of peripheral aromatization. Although free fractions of testosterone and estradiol are increased, total hormone levels are decreased due to decreased SHBG concentrations, and prolactin may be increased along with TSH in response to increased hypothalamic thyrotropin-releasing hormone. As a consequence, about 80% of women with hypothyroidism present menstrual disturbances or irregularities.\n
\nTreatment recommendations\nThe recommendations are very clear in treating overt hypothyroidism before and during pregnancy.  All women with a TSH greater than 10.0 mU/L should start treatment even when fT3/fT4 are within ranges. \nIf starting an IVF Treatment, it is recommended to measure TSH and TPO/TgAb in all women. Women with TSH > 4.0 mIU/L should start treatment to TSH < 2.5 mIU/L, and women with TAI and TSH levels between 2.5 and 4 mIU/L could benefit from treatment on a case-by-case basis to optimize embryo development. All Hyperthyroid patients are adequately treated before IVF Treatment.\nHyperthyroidism - Treatment Options\nSeveral options exist to treat hyperthyroidism: radioiodine ablation (RAI), surgical thyroidectomy, or antithyroid drug (ATD) therapy; in pregnancy, the first method is contraindicated, as well as in the 6 months before conception. As RAI was associated with the worsening of the ovarian reserve, it is important to adequately inform fertile women. Regarding surgery, the optimal time to perform this procedure is during the second trimester, followed by a gradual disappearance of TSH receptor antibodies. Considering ATD, propylthiouracil (PTU) is the preferred drug in the first 16 weeks of pregnancy because of the possibility of teratogenic effects of carbimazole and methimazole. \nFetal hyperthyroidism caused by the cross-placental passage of TRAb could appear at or after week 20 of pregnancy, so careful monitoring is required, and maternal fT4 levels should be kept in the upper third of the normal non-pregnant reference range. Finally, fetal hypothyroidism may also be expected due to overtreatment with the antithyroid drug.\n
\nThyroid and Male Fertility\nHuman testes have two main functions: androgen production and spermatogenesis. Thyroid hormones have their nuclear receptors expressed within the testis. Several endocrine and metabolic diseases are involved in male infertility, such as hypogonadism, diabetes, obesity, and adrenal dysfunction. Beyond these conditions, thyroid dysfunction may affect male fertility, too. Congenital hypothyroidism does not cause impaired development of the male reproductive system, although, on the other hand, if not properly treated with replacement therapy, it causes delayed sexual maturation.  The treatment of hypo- and hyperthyroidism is associated with an improvement in testis function.\nHyperthyroidism is also associated with the reduction of sperm concentration, motility, and impairment of sperm morphology, as well as a reduction of semen volume.  The treatment of thyrotoxicosis improves sperm motility, without significant changes in sperm morphology and count. Moreover, high levels of thyroid hormones can cause sperm DNA damage and infertility. Indeed, high levels of T3 and T4 promote an increase in reactive oxygen species (ROS) and, consequently, oxidative stress. \nConclusions:\nInfertility affects millions of people during reproductive age worldwide. Male and female factors on this condition contribute similarly (20–30%), and the endocrine system plays a role in this condition. Among endocrine conditions, thyroid dysfunction is frequently associated with female infertility, with emerging evidence on male fertility, and ART outcomes are influenced as well. Thyroid function should, therefore, be carefully monitored in both males and females, in couples seeking spontaneous pregnancy as well as ART, as treatment is generally immediate and likely to improve chances of success.\n

Understand the critical role thyroid health plays in fertility treatments and overall reproductive success.

Why Thyroid Function Matters in Fertility Treatments