**Core Concept**
Poly cystic ovarian syndrome (PCOS) is a complex endocrine disorder characterized by ovulatory dysfunction, hyperandrogenism, and polycystic ovarian morphology. This syndrome is a common cause of infertility and is often associated with metabolic complications such as insulin resistance and obesity.

**Why the Correct Answer is Right**
The characteristic features of PCOS include hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology. Hyperandrogenism is caused by an excess of androgens, which can be due to an increase in the production of androgens by the ovaries or an increase in the conversion of testosterone to dihydrotestosterone (DHT) by the enzyme 5-alpha-reductase. Ovulatory dysfunction is often due to an irregularity in the hypothalamic-pituitary-ovarian axis, leading to anovulation or oligo-ovulation. Polycystic ovarian morphology refers to the presence of multiple small cysts in the ovaries, which can be detected on ultrasound.

**Why Each Wrong Option is Incorrect**
* **Option A:** Infertility is a common feature of PCOS, so this option is incorrect.
* **Option B:** Obesity is a common comorbidity of PCOS, so this option is incorrect.
* **Option D:** Insulin resistance is a common metabolic complication of PCOS, so this option is incorrect.

**Clinical Pearl / High-Yield Fact**
PCOS is often associated with a metabolic syndrome, which includes insulin resistance, hypertension, and dyslipidemia. This syndrome increases the risk of developing type 2 diabetes and cardiovascular disease.

**Correct Answer: D. Regular menstrual cycles.**