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Why can the timing of ovulation be harder to predict in irregular menstrual cycles?

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Detailed cross-sectional illustration of a human ovary showing the stages of follicle development, ovulation, and corpus luteum formation, with labeled structures including primordial, primary, secondary, and mature follicles, a ruptured follicle releasing an ovum, and corpus luteum and albicans. An inset at the bottom shows the ovary's location in the female reproductive system. — ovary The steps of ovulation, beginning with a dormant primordial follicle that grows and matures and is eventually released from the ovary into the fallopian tube.

In women with irregular menstrual cycles, the timing of ovulation is often difficult to predict because the length of the proliferative phase of the cycle is typically prolonged.1

While the secretory phase of the cycle generally remains consistent in length, the variability in the duration of the proliferative phase—the period leading up to ovulation—makes the exact date of egg release uncertain. Because ovulation is driven by a complex interplay of hormones from the pituitary gland and the ovary, any disruption to this rhythm can shift the timing of the cycle. Even in women who are generally regular, the date of ovulation can still vary unexpectedly, further complicating predictions.1