Menstrual cycle characteristics and fecundability in a North American preconception cohort

The aim of this study was to evaluate the association between menstrual cycle characteristics in early life and adulthood and fecundability.

Pregnancy Study Online (PRESTO) is an Internet-based preconception cohort study of pregnancy planners from the United States and Canada. During the preconception period, we enrolled 2189 female pregnancy planners aged 21-45 years who had been attempting conception for ≤6 cycles. Women self-reported menstrual cycle characteristics via an online baseline questionnaire, and pregnancy status was ascertained through bimonthly follow-up questionnaires. Proportional probabilities models were used to estimate fecundability ratios (FRs) and 95% confidence intervals (CIs), adjusting for potential confounders.

Compared with usual menstrual cycle lengths of 27-29 days, cycle lengths of <25 (FR = 0.81, 95% CI: 0.54-1.22) and 25-26 days (FR = 0.92, 95% CI: 0.75-1.14) were associated with reduced fecundability. Compared with women who reached menarche at the age of 12-13 years, those who reached menarche at <12 years had reduced fecundability (FR = 0.87, 95% CI: 0.76-0.99). Women whose cycles never regularized after menarche (FR = 0.93, 95% CI: 0.81-1.06) had slightly reduced fecundability compared with women whose cycles regularized within 2 years of menarche. Bleed length and heaviness of bleeding were not appreciably associated with fecundability.

Menstrual cycle characteristics, specifically cycle length and age at menarche, may act as markers of fertility potential among pregnancy planners.