Final answer:
The most common cause of DUB in women of childbearing age is ovulatory dysfunction due to PCOS, which leads to hormonal imbalances and can prevent ovulation.
Step-by-step explanation:
The most common cause of dysfunctional uterine bleeding (DUB) in women of childbearing age is ovulatory dysfunction. Among the listed options, polycystic ovary syndrome (PCOS) is a major contributor to ovulatory dysfunction that can lead to DUB. PCOS is known for causing hormonal imbalances which can interfere with normal ovulation, leading to irregular menstrual cycles and anovulatory cycles, where ovulation does not occur.