Menstrual bleeding, cycle length, and follicular and luteal phase lengths in women without known subfertility: A pooled analysis of three cohorts

Abstract

Background: There is variability between women for days of menstrual bleeding, cycle lengths, follicular phase lengths, and luteal phase lengths, related to age and parity.Objective: To describe total cycle length; anovulatory cycles; follicular and luteal phase lengths; and days and intensity of menstrual and non-menstrual bleeding in women without known subfertility over the course of 1 year.Methods: 581 women (3,324 cycles) with no known subfertility (18-40 years of age) were followed for up to 1 year. Women recorded vaginal bleeding and mucus discharge daily. We used the peak day of cervical mucus as the estimated day of ovulation and the last day of the follicular phase. We used generalised linear mixed models stratified by age and parity to describe menstrual cycle parameters. Results:The majority of women were <30 years of age (74.5%), non-Hispanic White (88.6%), and nulliparous (70.4%). The mean menses length was 6.2 (1.5) days, median 6; cycle length 30.3 (6.7) days, median 29; follicular phase length 18.5 (6.5) days, median 17; and luteal phase length 11.7 (2.8) days, median 12. Nulliparous women aged ≥30 years vs nulliparous women aged < 30 had shorter cycles (29.2 days, 95% confidence interval (CI) 27.8, 30.7 vs 31.5 days, 95% CI 30.8, 32.2) and shorter follicular phases (17.6 days, 95% CI 16.2, 18.9 vs 19.6 days, 95% CI 18.9, 20.2). Among all women, within-woman differences between the longest and shortest menses length >3 days, total cycle length >7 days, follicular phase >7 days, and luteal phase >3 days were found in 11.6%, 43.0%, 41.7%, and 58.8% of women, respectively. Conclusions:Our findings confirm variability between women of menstrual cycle parameters related to age and parity, and also highlight within-woman variability in the follicular and luteal phases. K E Y W O R D S follicular phase, luteal phase, menstrual cycle, menstruation, ovulation, peak day A commentary on this paper appears on pages 328-330 Additional supporting information may be found online in the Supporting Information section. How to cite this article: Najmabadi S, Schliep KC, Simonsen SE, Porucznik CA, Egger MJ, Stanford JB. Menstrual bleeding, cycle length, and follicular and luteal phase lengths in women without known subfertility: A pooled analysis of three cohorts.

Challenges and future directions in menstrual cycle research

“…The landmark study by Treloar of 2700 women and approximately 250 000 menstrual cycles gathered over a maximum of 30 years has never been replicated and still provides useful estimates of menstrual cycle length and variability over time. The article by Najmabadi and colleagues in this month's Paediatric and Perinatal Epidemiology adds to this literature by combining data from several cohort studies to examine patterns in menstrual cyclicity and menstrual bleeding, and most importantly, follicular and luteal phase length. An important contribution of Najmabadi's study, which the Treloar study could not address, is the description of phase lengths and variability in over 500 women.…”

“…For example, one large app study includes a sample which is mostly White, while another app study does not describe the racial/ethnic distribution of the sample at all . The Najmabadi study, which did not employ an app, also includes a sample that is mostly White . Cycle length may differ by race or ethnicity, and associations between exposures and menstrual cycle length may differ within racial groups.…”

“…On the other hand, women with irregular cycles may be less represented in a given research study, as some studies require “regular cycles” to enrol. Relatedly, some studies depend on fertility awareness methods which may be designed specifically for women with regular, predictable menstrual cycles. Again, both app‐based and traditional epidemiologic studies face the same challenge of identifying who is “volunteering” to participate in their research in order to identify the potential for selection bias or a lack of generalisability.…”

“…An additional source of potential selection bias is that menstrual cycle studies often focus on women trying to conceive a pregnancy (eg references and ). This may be because fertility is the primary outcome of interest, or because menstrual cycles can only be studied in women who are not using hormonal birth control.…”

“…Again, regardless of whether an app is used, differences in measurements limit comparisons across studies. For example, studies often rely on women's self‐identification of a menstrual period onset to define the beginning of a menstrual cycle (as in ). While this is likely to be a valid measure for most cycles, some fraction (anywhere from 5% to 36% ) will have intermenstrual bleeding (bleeding that occurs between menstrual periods), which may influence her ability to recognise a menses, and may lead to inaccurate cycle length measurements.…”