Polycystic Ovary Syndrome (PCOS) is one of the most common endocrine disorders affecting women of reproductive age and represents a leading cause of anovulatory infertility. It is characterised by hyperandrogenism, insulin resistance, and disrupted folliculogenesis, all of which adversely affect ovarian function and oocyte quality. These alterations create a hormonally and metabolically unfavourable ovarian environment, impairing normal follicle development and ovulation.
Among the therapeutic strategies used to manage PCOS, metformin, an insulin-sensitising agent widely prescribed for type 2 diabetes, has attracted considerable interest. Although initially introduced for metabolic control, metformin has demonstrated potential reproductive benefits. Its ability to modulate insulin levels and ovarian function suggests a broader role in improving follicular development and oocyte competence in women with PCOS.
Pathophysiology of PCOS and Disrupted Folliculogenesis
The pathogenesis of PCOS involves a complex interaction between endocrine and metabolic abnormalities. Insulin resistance leads to compensatory hyperinsulinaemia, which stimulates ovarian theca cells to produce excess androgens while suppressing hepatic sex hormone-binding globulin synthesis. Elevated androgen levels interfere with normal follicular maturation, resulting in the accumulation of small antral follicles and failure of dominant follicle selection. This arrested follicular development contributes to chronic anovulation and compromised oocyte maturation.
Mechanism of Action of Metformin in PCOS
Metformin improves insulin sensitivity by decreasing hepatic gluconeogenesis and enhancing peripheral glucose uptake. In women with PCOS, this reduction in circulating insulin levels leads to decreased ovarian androgen production and partial restoration of endocrine balance. By alleviating hyperinsulinaemia-driven hyperandrogenism, metformin creates conditions that are more conducive to normal follicular recruitment and growth. Additionally, experimental studies suggest that metformin may exert direct effects on ovarian cells by modulating intracellular signalling pathways involved in energy metabolism and cell proliferation.
Role of Metformin in Insulin Sensitivity and Hormonal Regulation
Insulin resistance is a key feature of PCOS and contributes to hyperinsulinaemia, which stimulates ovarian androgen production and disrupts normal reproductive hormone regulation. Metformin improves insulin sensitivity by reducing hepatic glucose production and enhancing peripheral glucose uptake, leading to lower circulating insulin levels. This reduction decreases ovarian androgen synthesis and increases sex hormone–binding globulin levels, helping to restore hormonal balance. Improved insulin sensitivity also creates a more favourable intrafollicular environment, enhancing follicular development and oocyte maturation. Overall, metformin’s metabolic and hormonal effects play an important role in improving reproductive function in women with PCOS.
Effects of metformin on ovarian follicular development
Several studies have shown that metformin may help normalise folliculogenesis in women with PCOS. By decreasing luteinising hormone (LH) levels and hyperinsulinaemia, metformin promotes the selection and growth of a dominant follicle. It can reduce the number of small antral follicles and increase the chances of ovulation. This effect is particularly beneficial for women undergoing ovulation induction or assisted reproductive technologies (ART).
Impact of metformin on oocyte quality
Oocyte quality in PCOS is frequently compromised due to exposure to an abnormal hormonal and metabolic follicular environment. Metformin appears to improve oocyte competence by enhancing glucose metabolism within the follicle and reducing oxidative stress. Improved insulin sensitivity may support mitochondrial function and cytoplasmic maturation of the oocyte. Several clinical studies have reported improved fertilisation rates and embryo quality in metformin-treated PCOS patients, although findings remain variable.
Clinical Implications and Fertility Outcomes
While metformin alone may not consistently induce ovulation, it is commonly used as an adjunct to ovulation-induction agents such as clomiphene citrate or letrozole. In ART settings, metformin pre-treatment has been associated with a reduced risk of ovarian hyperstimulation syndrome (OHSS) and, in selected populations, improved pregnancy outcomes. However, the degree of benefit appears to depend on individual metabolic profiles, highlighting the need for personalised treatment strategies.
