Elsevier

Annals of Epidemiology

Volume 26, Issue 7, July 2016, Pages 482-487.e1
Annals of Epidemiology

Original article
Menstrual cycle characteristics and fecundability in a North American preconception cohort

https://doi.org/10.1016/j.annepidem.2016.05.006Get rights and content

Abstract

Purpose

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

Methods

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.

Results

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.

Conclusions

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

Introduction

The menstrual cycle is characterized by a series of feedback responsive processes in the hypothalamic–pituitary–ovarian axis. These changes allow for the release of a mature egg from the dominant ovarian follicle and the development of a receptive endometrial lining that can support a pregnancy [1]. Menstrual patterns are a marker of ovarian and hormonal function and may be related to fecundity, the biologic capacity for reproduction [2]. Women with irregular cycles may have longer time to pregnancy due to higher risk of anovulation [2], an underlying disorder of the hypothalamic–pituitary–ovarian axis or the uterus [3], and/or difficulty timing intercourse to the fertile window [4].

Several studies support an association between cycle length and fecundity, even after controlling for age. Short cycles may reflect ovarian aging [5] or a narrow fertile window and are associated with higher risk of anovulation [2] and lower fecundability compared with normal length cycles [6], [7], [8]. However, evidence assessing the association between long menstrual cycles and fecundability is inconsistent. In an in vitro fertilization (IVF) cohort, egg donors with regular menstrual cycles of 34–35 days had lower gonadotropin medication requirements, improved oocyte quality, and better cycle success compared with donors with menstrual cycles of 27–28 days [9]. Cycle length has been positively associated with pregnancy rates in women undergoing IVF [10] and with improved fecundability among pregnancy planners [6] but also with increased risk of anovulation [2] and reduced fecundability [7], [8]. Long irregular cycles may reflect underlying gynecologic disease, and inconsistencies in prior studies may relate to varying exclusion criteria (e.g., women with irregular cycles or women whose menstrual characteristics are obscured by recent hormone use). Differing study designs and small study sizes may also account for inconsistencies in the literature.

Bleed length and heaviness of bleeding may act as markers of endometrial development. In a study of regularly menstruating, healthy females in the United States, anovulatory cycles were followed by lighter blood loss and shorter bleed length compared with ovulatory cycles [11]. These findings are supported by other prospective cohort studies that have found an association between short cycle length and lower fertility [7], [12]. However, a Danish preconception cohort study found only slightly lower fecundability among women with short bleeds or light menstrual flow [6].

In a cohort of North American pregnancy planners, we examined early life menstrual cycle characteristics (age at menarche and time until cycle regularity) and current menstrual cycle characteristics (irregular cycles, cycle length, bleed length, and heaviness of bleed) in relation to fecundability.

Section snippets

Study population

Pregnancy Study Online (PRESTO) is an Internet-based preconception cohort study of pregnancy planners in the United States and Canada. The study methodology has been described in detail elsewhere [13]. Recruitment began in June 2013 and was conducted primarily through banner advertisements on social media and health-related websites. Eligible women were aged 21–45 years, in a stable relationship with a male partner, and not using contraception or fertility treatments. The Institutional Review

Results

The analysis of early life menstrual cycle characteristics and fecundability includes 2189 women contributing 9832 cycles and 1355 pregnancies. Over 23% of participants reported menarche at <12 years of age. Most women (51.4%) had cycles that regularized in <2 years, whereas 4.7% of women had cycles that took ≥4 years to regularize, and 21.8% never regularized.

The analysis of current menstrual cycle characteristics and fecundability includes 1260 regularly cycling women contributing 5719 cycles

Discussion

In this preconception cohort study, short cycle length, early age at menarche, and heavy menstrual bleeds were associated with reduced fecundability. Bleed length and time until cycle regularity were not appreciably associated with fecundability. Our results were imprecise due to small numbers but were also reasonably consistent with those of prior literature.

Previous studies have reported an association between short cycle length and fecundability [6], [7], [8], [20]. In a Danish preconception

Acknowledgments

The authors acknowledge the contributions of PRESTO participants and staff. They thank Mr. Michael Bairos for his technical support with developing the Web-based infrastructure of PRESTO. The authors are grateful to Dr. Frederic Montoya and Dr. Heather Bromberg for their generous donation of FertilityFriend.com memberships. They also thank Dr. Kristen A. Hahn and Ms. Alina Chaiyasarikul for their technical assistance and instrumental support of the study.

This study was funded by NICHD grant

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