Does ovulation become less consistent during the menopausal transition?

The claim is broadly consistent with longitudinal endocrine data on the menopausal transition. Ovulation becomes progressively less predictable, and this likely contributes to—though does not alone prove—the marked variability in ovarian hormone output.

Clinical and hormonal evidence

• In prospective daily-urine monitoring of women aged 43–53 years, ovulatory-appearing cycles fell from 80.9% at baseline to 64.7% after 3 years. In a separate 5-year cohort, >60% of late-perimenopausal cycles were anovulatory.
• This is stage-dependent rather than absolute: most early-transition cycles retain luteal activity, whereas anovulation becomes substantially more prevalent in late perimenopause. Even among cycles lasting ≥60 days, about one-quarter remained ovulatory.
• Estradiol-related output is erratic across the transition rather than declining smoothly. Anovulatory cycles show lower estrone-conjugate output than ovulatory cycles, and cycle length also becomes more variable, particularly when luteal activity is absent.

Mechanistic interpretation

• Ovulation produces the corpus luteum, the main source of luteal progesterone. Alternation between ovulatory and anovulatory or delayed-ovulatory cycles therefore provides a biologically coherent explanation for swings between higher and low/absent progesterone output.
• Progesterone-metabolite excretion (PdG) declines through the transition, including in apparently ovulatory cycles, indicating that reduced luteal progesterone can occur independently of complete anovulation.
• Similarly, inconsistent ovulation likely contributes to estradiol variability, but changing follicular dynamics and menopausal stage also contribute.

Bottom line

• Ovulation increasingly becomes intermittent during perimenopause, especially late in the transition. This plausibly drives greater cycle-to-cycle estradiol and progesterone variability, although direct within-person causal quantification remains limited. Ovulation—and therefore possible conception—can still occur before the final menstrual period.