Polycystic ovary syndrome (PCOS) is the most common endocrine disorder among women of reproductive age, and is a complex and variable condition involving alterations in reproductive, hormonal and metabolic processes. It has a clinical picture that often includes irregular menstruation, hyperandrogenism, hirsutism, acne, infertility and polycystic oviary morphology. The syndrome is closely linked to genetic susceptibility, dysfunction of the hypothalamo-pituitary-ovarian axis, and metabolic abnormalities. The clinical features are very variable, with some women having their main complaints of reproduction and others having a high level of metabolic complication. Commonly used Rotterdam diagnostic criteria include ovulatory dysfunction, hyperandrogenism and polycystic ovarian morphology (after excluding other endocrine diseases). Since PCOS is linked to metabolic abnormalities and reproductive issues during the female life span, its early detection and detailed investigation are still important aspects of women's health care [1-3].

Insulin resistance plays an important role in the metabolic changes associated with PCOS, and is involved in the development of various reproductive and endocrine abnormalities. Decreased insulin sensitivity leads to compensatory hyperinsulinemia, which can lead to ovarian production of more androgens and less production of sex hormone binding globulin in the liver, creating higher circulating free androgen levels. The hormonal changes disrupt the normal development of the follicles and the functioning of the ovulation process leading to irregular menstrual periods and reproductive dysfunction. Insulin resistance is also commonly seen in obese women, but it can also be seen in women with PCOS who are within the normal weight range, which indicates that, intrinsic defects in insulin signaling play an important role in the metabolic phenotype. There is a risk of development of impaired glucose tolerance, type 2 diabetes mellitus, dyslipidaemia and other cardiometabolic disorders in the presence of chronic insulin resistance. Thus, it is important to understand the metabolic features of women with PCOS to assess their reproductive health and clinical outcomes to manage them in the long-term [4-6].

Menstrual irregularities are one of the most obvious symptoms of PCOS, and often manifest as either oligomenorrhea or amenorrhea, or as long periods between periods or irregular periods. The disturbances in these abnormalities are mainly related to chronic anovulation and abnormalities in the physiological regulation of ovarian follicular development. The abnormalities in gonadotropin secretion and ovarian steroidogenesis may result from hyperinsulinemia and androgen excess, thus further disrupting normal menstrual cyclicity. Insulin resistance and menstrual disturbances have been studied more closely, due to the fact that menstrual disturbances in terms of menstrual frequency and length of the cycle can serve as a marker of metabolic disorder. Menstrual expression, however, is very variable across women with the condition, and BMI, age, androgen levels and metabolic traits may all play a role in determining its severity. These interactions are important to recognize in helping to identify women who need more in-depth metabolic assessment and individualized reproductive health care [7-9].

Thyroid dysfunction represents an additional endocrine abnormality that may coexist with PCOS and influence menstrual and metabolic health. Thyroid hormones regulate cellular metabolism, reproductive hormone activity, ovarian function, and normal menstrual cycle physiology. Hypothyroidism and subclinical hypothyroidism may be associated with menstrual disturbances, impaired ovulation, altered lipid metabolism, and changes in insulin sensitivity. Women with PCOS and coexisting thyroid abnormalities may therefore exhibit overlapping reproductive and metabolic manifestations, complicating clinical evaluation. However, thyroid dysfunction can independently cause menstrual irregularities and must be differentiated from abnormalities attributable to PCOS. Despite growing interest in these endocrine relationships, uncertainty remains regarding the independent and combined associations of insulin resistance and thyroid dysfunction with menstrual disturbances. Understanding these associations may contribute to better endocrine assessment, individualized management, and identification of women at increased reproductive and metabolic risk. Therefore, the present study was designed to determine the association between insulin resistance, thyroid dysfunction, and menstrual irregularities among women diagnosed with PCOS.

This analytical cross-sectional study was designed to investigate the association between insulin resistance, thyroid dysfunction, and menstrual irregularities among women diagnosed with polycystic ovary syndrome (PCOS) in DHQ Hospital Mandi Bahauddin, Pakistan. The study covered a period of 18 months, from January 2025 to June 2026. The study focused on identifying metabolic and endocrine abnormalities among women with PCOS and evaluating their relationship with menstrual cycle disturbances. Demographic information, clinical characteristics, menstrual history, and biochemical parameters were assessed using a structured data collection proforma. The sample size was determined using the WHO formula for estimating a single population proportion, considering a 95% confidence level, an anticipated prevalence of thyroid dysfunction of 40.6% among women with PCOS [10], as reported in previous literature, and an absolute precision of 8%. The minimum calculated sample size was approximately 145 participants. Accordingly, the study sample size was set at 145 women diagnosed with PCOS. A non-probability consecutive sampling technique was specified for participant recruitment, whereby eligible women presenting during the study period were considered for inclusion until the required sample size was achieved. Patients with PCOS diagnosed by the modified Rotterdam criteria who were women aged 18–40 years were included. At least two of three clinical or biochemical signs of hyperandrogenism, polycystic ovarian morphology on ultrasonography, and ovulatory dysfunction (after excluding other possible causes of these features) were required for diagnosis. For comparative analysis, women with documented history of menstrual cycle abnormalities and those with regular cycles were allowed. Women were considered for participation if they had signed an informed consent. Pregnant women, women who had been given a hysterectomy or bilateral oophorectomy, and women with breast-feeding were excluded, as were women who had reached menopause. Other exclusion criteria were known hyperprolactinemia, non-classical congenital adrenal hyperplasia, Cushing syndrome, androgen-secreting tumors and other conditions that can also be causative of menstrual dysfunction. Women on medications known to affect insulin sensitivity, thyroid hormone levels, or menstrual cyclicity (such as metformin, hormonal contraceptives, systemic corticosteroids, and thyroid medications) were considered for exclusion because these medications could affect the biochemical assessment. There was no automatic exclusion of women with prior thyroid disease as thyroid dysfunction was a key exposure of interest; those receiving thyroid-directed treatment were excluded from the untreated biochemical comparison. Demographic and clinical information was collected using a structured proforma. The variables recorded were age, marital status, weight, height, body mass index (BMI), duration of PCOS, family history of PCOS, family history of diabetes mellitus and clinical signs of hirsutism and acne. The weight of the body was taken in the unit of kilogram and height was taken in the unit of meter. The BMI was computed as the ratio of weight (kg) to the square of height (m) Underweight, normal weight, overweight and obesity status were defined according to predetermined BMI cut-off points. Menstrual histories were obtained in a detailed manner, including cycle length, frequency, regularity and duration of menstrual disturbances. Menstrual cycles were classified according to predefined criteria. The regular cycles were those that appeared at intervals of 21–35 days. Oligomenorrhea was classified as menses periodicity more than 35 days, and amenorrhea as lack of menstruation for a period of at least 90 days. Menstruation was counted as periods that took place in an interval of less than 21 days. The presence of menstrual irregularity was determined by the presence of any of these abnormal menstrual patterns. The participants were divided into two categories: Regular and Irregular menstrual cycle groups for further comparison. For the estimation of fasting plasma glucose and fasting serum insulin, venous blood samples were taken after an 8-12 hour overnight fasting. Fasting glucose was measured in mg/dl and fasting insulin in µIU/dl. The Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) was used to assess insulin resistance. In the current analysis, HOMA-IR ≥2.5 was considered insulin resistant and <2.5 was non-insulin resistant. The threshold was not considered as a standard diagnostic cut-off value. Participants were randomly assigned to the insulin-resistant or non-insulin-resistant group and their demographic data, thyroid profiles and menstrual characteristics were compared between the two groups. Thyroid function tests included serum TSH and serum free thyroxine (FT4). Where available, free triiodothyronine (FT3) concentrations were also considered. The thyroid function was classified using laboratory reference intervals and the TSH and free thyroid hormone levels. Those who had TSH and FT4 levels within the reference range were considered to be euthyroid. Subclinical hypothyroidism was diagnosed when TSH was elevated, with a normal FT4 level, and overt hypothyroidism was diagnosed when TSH was elevated and FT4 was reduced. TSH suppression was evaluated in the presence or absence of higher levels of free thyroid hormone for hyperthyroid patterns. The subjects were divided into two groups (euthyroid and thyroid dysfunction groups) for comparative analysis. This association between thyroid function and insulin resistance and menstrual abnormalities was then assessed. The data were analysed with IBM SPSS Statistics version 25.0. The continuous variables, such as age, BMI, fasting blood glucose, fasting serum insulin, HOMA-IR, TSH, FT4 and menstrual cycle length were summarized as mean ± SD for approximately normally distributed data and median and inter quartile range for skewed distributions. Categorical variables such as insulin resistance, thyroid dysfunction, menstrual irregularities and clinical manifestations were presented as frequency and percentage. Continuous variables were checked for normality using the Shapiro–Wilk test and graphically. To investigate the relationships between insulin resistance, thyroid hormone/antibodies and menstrual irregularity, the chi square test or Fisher's exact test, whichever was appropriate, was used. Independent-samples t-tests or Mann–Whitney U tests were recommended for comparing continuous variables between groups. Pearson or Spearman's correlation coefficient was used to assess the correlation between HOMA-IR, TSH, menstrual cycle length and BMI according to the distribution of the variables. A binary logistic regression was used to determine the independent effects of insulin resistance and thyroid dysfunction on menstrual irregularity, adjusting for age and BMI. Odds ratios (AORs) with 95% confidence intervals were to be reported. A p value < 0.05 was regarded as a statistically significant level of significance.

The study population consisted of 145 women with PCOS, mean age 27.84 ± 5.00 years. The majority of the participants (71.0%) were in the age group of 18-30 years. The BMI of the mean of the study population was 29.75 ± 4.40 kg/m², in which 42.8% of the population was overweight and 45.5% was obese. The mean period of PCOS was 4.17 ± 2.49 years. The most common clinical findings were hirsutism (63.4%) followed by acne (42.1%).

Table 1. Demographic and Clinical Characteristics of Women with PCOS (n=145)

The mean fasting blood glucose level was 95.00 ± 8.71 mg/dL, and the mean fasting insulin and HOMA-IR were 12.11 ± 5.04 µIU/mL and 2.83 ± 1.17, respectively. Insulin resistance was defined as a HOMA-IR value of ≥2.5 and present in 82 participants (56.6%). Thyroid dysfunction was noted in 33 women (22.8%) mainly subclinical hypothyroidism.

Table 2. Biochemical Characteristics, Insulin Resistance and Thyroid Function

Women who had insulin resistance had more menstrual irregularities. Oligomenorrhea was the most common menstrual disturbance, and occurred in 44 women with insulin resistance but in only 20 women without insulin resistance. In all, 59 of 82 insulin-resistant women (72.0%) experienced menstrual irregularities, while 27 of 63 non-insulin-resistant women (42.9%) did not. This association was significant statistically (p<0.001).

Table 3. Association Between Insulin Resistance and Menstrual Irregularities

Overall menstrual irregularity versus regular menstruation: Pearson's chi-square test, p<0.001. Percentages are calculated within insulin-resistance groups.

Among women with thyroid dysfunction, 29 (87.9%) vs. 57 (50.9%) of the euthyroid women had irregular periods. Women experiencing thyroid dysfunction were more likely to have oligomenorrhea. The mean HOMA-IR was also higher in the thyroid dysfunction group (3.16 ± 0.98 versus 2.74 ± 1.21; p=0.044). There was no significant difference in BMI between the groups.

Table 4. Association Between Thyroid Dysfunction and Menstrual Irregularities

Categorical comparison: chi-square test. Continuous comparisons: Welch's independent samples t-test.

Spearman correlation analysis showed that BMI was positively associated with HOMA-IR (ρ=0.367, p<0.001). The serum TSH was weakly positively correlated with menstrual cycle length (ρ=0.182, p=0.028). There were no significant linear relationships between HOMA-IR and TSH, and HOMA-IR and menstrual cycle length. After adjusting for age and BMI, insulin resistance (AOR 3.69, 95% CI 1.66–8.23; p=0.001) and thyroid dysfunction (AOR 6.23, 95% CI 1.98–19.53; p=0.002) were both independent associations with menstrual irregularities.

Table 5. Correlation and Multivariable Logistic Regression Analysis

Part A. Correlation analysis

Part B. Multivariable logistic regression

Figure 1. Prevalence of Menstrual Irregularities According to Combined Insulin Resistance

and Thyroid Dysfunction Status

Polycystic ovary syndrome (PCOS) is a complex endocrine and metabolic disorder affecting women of reproductive age, characterized by ovulatory dysfunction, hyperandrogenism, insulin resistance, and variable metabolic disturbances. The pathophysiology of PCOS involves interactions among genetic susceptibility, ovarian steroidogenesis, metabolic dysfunction, and hormonal regulatory mechanisms. Insulin resistance plays a central role in the development and progression of metabolic abnormalities, while thyroid dysfunction may contribute to disturbances in reproductive hormone regulation and menstrual cyclicity. The coexistence of these endocrine abnormalities can complicate the clinical presentation of PCOS and emphasizes the importance of comprehensive metabolic and hormonal assessment. Contemporary evidence supports a multidisciplinary approach that considers reproductive, metabolic, and long-term cardiovascular health rather than focusing exclusively on ovarian manifestations [11-13]. Insulin resistance is one of the most significant metabolic disorders linked to PCOS and can happen even when there's no obesity, but excess weight may make insulin resistance worse. Compensatory hyperinsulinemia associated with insulin resistance leads to increased production of ovarian androgens and decreased production of sex hormone-binding globulin in the liver. These changes lead to elevated levels of free androgens in the circulation and could affect normal follicular maturation and ovulation. This hormonal imbalance can lead to irregular periods, anovulation and reproductive disorders. Insulin resistance is also linked to other abnormalities such as dyslipidaemia, impaired glucose tolerance and higher risk of type 2 diabetes mellitus. Insulin resistance could become a vicious cycle due to the interaction of insulin signaling abnormalities with androgen excess and is therefore important in the clinical evaluation of women with PCOS [14-16]. Menstrual irregularity is one of the key clinical features of PCOS and often manifests as oligomenorrhea, amenorrhea and irregular and unpredictable periods. These are mostly caused by a disturbance in the development of the follicles and chronic failure of ovulation. Hyperinsulinemia can have a role in menstrual abnormalities due to its effects on ovarian steroidogenesis, gonadotropin activity and androgen availability. Insulin resistance and menstrual dysfunction are clinically relevant because although menstrual disturbances are a part of a more adverse metabolic profile, the menstrual history is not a good marker of the level of insulin resistance. In addition, the severity of the menstrual disorder fluctuates between women with PCOS due to the differences in their endocrine phenotype, body composition, metabolic profile and their individual hormonal response. Earlier detection of menstrual dysfunction is vital to the assessment of reproductive health, to solve fertility issues and to minimise the problems associated with long-term anovulation [15-17]. An additional important endocrine consideration in women with PCOS-like symptoms is thyroid dysfunction. Thyroid hormones affect the menstrual cycle, metabolism, ovarian function and reproductive hormone metabolism. Low thyroid activity (hypothyroidism) with an elevated concentration of thyroid-stimulating immunoglobulin (TSI) can cause irregular periods and trouble with ovulation. Subclinical hypothyroidism has also been studied for insulin resistance, dyslipidaemia and pregnancy complications in women with polycystic ovary syndrome (PCOS). But, the link between thyroid disorders and PCOS is complex, and not always clear that there's a direct causal cause. One important diagnostic point to note is that thyroid dysfunction can also cause menstrual disturbances and can mimic some of the signs and symptoms of a PCOS. Thus, assessing thyroid function is important when considering reproductive and metabolic abnormalities, especially when women have chronic menstrual irregularities or infertility [18, 19]. The association between insulin resistance and thyroid function and menstruation can be further complicated by obesity and body composition changes. An association of increased visceral adiposity with decreased insulin sensitivity, chronic low grade inflammation, and changes in adipokine signaling may further contribute to metabolic dysfunction in PCOS. However, these reproductive abnormalities and insulin resistance can be seen in women with a normal BMI, and BMI is not a good indicator of metabolic risk. The syndrome is presented in a variety of ways, which include inflammatory pathways and impaired insulin signaling and ovarian endocrine regulation. These mechanisms support the notion of patient-specific clinical evaluation of a patient rather than using body weight or a single biochemical variable. Balanced nutrition, regular physical activity and behavioral change that is sustainable over time are core pillars of PCOS management, and offer advantages for metabolic health, menstruation and general well-being [20]. The treatment for PCOS should be multi-faceted and should include the treatment of reproductive symptoms and metabolic disorders. Evaluation of glycemic control, cardiovascular risk factors, menses history and endocrine abnormalities may help in guiding the appropriate management and long-term follow-up. In guideline on PCOS recommends that glycemic evaluation be performed in women with PCOS and that the oral glucose tolerance test (OGTT) should be used for assessing glycemic status in women with PCOS. Insulin resistance is a known characteristic of PCOS, but clinical measurement of insulin is not suggested routinely as no current assays are standardized and of limited clinical value. Assessment of thyroid function is continuing to be valuable in the diagnostic work-up to rule out other causes of menstrual disturbances. Therapy should be tailored to the patient's reproductive objectives, metabolic risk, symptom severity and patient preference, and, if needed, coordinated between gynecologists and endocrinologists. Limitations and Future Research The cross-sectional design limits the ability to establish temporal or causal relationships between insulin resistance, thyroid dysfunction, and menstrual irregularities. Variability in HOMA-IR thresholds, laboratory reference ranges, and menstrual history assessment may also affect comparability across studies. Future prospective investigations with larger samples, standardized metabolic assessments, and longitudinal monitoring of menstrual function are required to clarify the independent and combined contributions of insulin resistance and thyroid abnormalities to PCOS-related reproductive dysfunction.

Insulin resistance, thyroid dysfunction, and menstrual irregularities are important and potentially interconnected features in the clinical assessment of women with polycystic ovary syndrome. Metabolic disturbances may contribute to altered ovarian function and ovulatory dysfunction, while coexisting thyroid abnormalities can further complicate menstrual regulation and reproductive health. Comprehensive assessment of glycemic status, thyroid function, and menstrual patterns is therefore important for identifying women who may benefit from individualized endocrine and gynecological management. Early recognition of associated metabolic and hormonal abnormalities, together with appropriate lifestyle interventions and targeted treatment, may help improve reproductive and long-term metabolic health. Further longitudinal studies are needed to establish the direction and clinical significance of these relationships.