Does having a long cycle mean you are less fertile?

Research shows that the characteristics of your menstrual cycle, such as the overall length of the cycle and the length of the bleed, is associated with fertility (Small CM, 2006).  Menstrual cycle patterns are an indicator of endocrine function.

It is unclear whether a history of cycle irregularity in early menstrual life—among women with regular cycles in adulthood—also predicts fertility potential across the reproductive years (Lauren A Wise, 2011).

What causes a long cycle?

Obesity has been associated with amenorrhea (lack of a period) and polycystic ovarian disease (PCOS). A high waist-to-hip ratio has been associated with infrequent cycles. One study of US college women found that heavier women had the greatest probability of having long menstrual cycles.

Cycle variability

In addition to the length of the cycle, the variability of the cycle length (by how many days the cycle length differs from cycle to cycle) the is also a predictor of fertility.