Thyroid Dysfunction Roles in Iraqi Women with Infertility: A Cross-sectional Study View PDF

The World Health Organization describes infertility as the inability of a couple to achieve pregnancy after one year of regular, unprotected sexual intercourse [1]. Globally, infertility affects an estimated 60 – 80 million individuals [2]. Primary infertility refers to a situation in which a couple has never been able to conceive, with reported rates ranging between 2% and 5%. In contrast, secondary infertility occurs when a couple who has previously conceived is unable to achieve another pregnancy, and it is estimated to affect approximately 20% of couples worldwide [2, 3].

Optimal hormonal balance and proper endocrine function are crucial for embryo implantation and the continuation of pregnancy. Thyroid hormones are closely linked with the reproductive system, although the exact mechanisms underlying this interaction are not yet fully clarified. Disorders of the thyroid gland are frequently associated with menstrual irregularities and reduced fertility. Thyroid hormones exert their effects by binding to specific receptors and activating transcription factors that are widely distributed across various tissues in the body. TSH regulates the production of thyroid hormones in the thyroid gland, but evidence suggests it also plays additional roles within the female reproductive system. Increased expression of thyroid hormone and TSH receptors in the receptive endometrium indicates their involvement in implantation, potentially through modulation of inflammatory mediators such as leukemia inhibitory factor, a key cytokine in female reproduction. The observed link between thyroid dysfunction and infertility suggests that thyroid hormones and TSH may influence both the endometrium and ovarian function through local (paracrine) mechanisms [4].

Thyroid hormones play a central role in regulating growth, metabolism, and overall cellular activity. In addition to gonadotropins such as Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin, they contribute significantly to the proper functioning of the female reproductive system and the maintenance of fertility [5- 7]. Both hypothyroidism and hyperthyroidism are well recognized for their association with menstrual disturbances, which can subsequently impair fertility. Abnormal thyroid function is a major contributor to menstrual disorders such as oligomenorrhea, amenorrhea, polymenorrhea, and menorrhagia. These disturbances are largely attributed to alterations in the hormonal milieu, including imbalances in estrogen, prolactin, and Gonadotropin-releasing hormone (GnRH), as well as disruptions in the normal pulsatile secretion of LH [8].

Thyroid hormones exert a direct influence on oocyte development, and maintaining normal thyroid function is essential for optimal fertilization outcomes. Evidence supports this relationship, as treatment of hypothyroid women with infertility has been shown to restore prolactin concentrations and normalize the LH response to GnRH. These hormonal corrections often reduce menstrual irregularities and improve the likelihood of natural conception. In women undergoing in vitro fertilization, serum levels of TSH may also serve as a predictive marker for treatment success or failure [9, 10].

In cases of thyrotoxicosis, menstrual disturbances such as oligomenorrhea and amenorrhea are frequently observed. Although circulating reproductive hormone levels may be elevated, ovulatory cycles can still occur in some women. The rise in LH, FSH, and estrogen metabolism is thought to result from increased activity of GnRH [11]. However, the characteristic mid-cycle LH surge may be diminished or entirely absent [12]. Additionally, studies have reported a marked increase in LH secretion—without a corresponding rise in FSH— following administration of thyrotropin-releasing hormone [13].

In women with thyrotoxicosis, levels of sex hormone–binding globulin are typically elevated, which alters the availability of circulating sex steroids [14]. Additionally, the metabolic clearance rates of testosterone and estradiol are reduced, leading to changes in their serum concentrations [15]. Some patients also exhibit enhanced peripheral aromatization of androgens to estrogens, further contributing to hormonal imbalance [16, 17].

This study aimed to evaluate the impact of thyroid dysfunction on Iraqi females experiencing both infertility types.