The purpose of this derived dataset was to analyze menstrual cycle lengths in relation to lunar calendar. This datafile of start and end date of 3324 menstrual cycles of 581 women is part of a combined dataset of three cohorts of heterosexually active women who received instruction in the Creighton Model FertilityCare System (CrM) through centres across the United States and Canada. The CrM has standardised protocols for teaching women how to observe, record, and interpret daily vaginal discharge from bleeding and cervical fluid on a daily diary, called a CrM chart, and to use these standardised observations to identify the estimated time of ovulation and days when intercourse is likely to result in pregnancy. The cohorts included: "Creighton Model Effectiveness, Intentions, and Behaviours Assessment" (CEIBA) (2009–2013), a prospective cohort of women without known subfertility, aimed to evaluate and classify pregnancy rates and pregnancy intentions during use of the CrM; "Creighton Model MultiCenter Fecundability Study" (CMFS) (1990–1996), a retrospective cohort of presumably fertile and subfertile women using CrM, aimed to assess the relationship between vulvar mucus observations and the day and cycle-specific probabilities of conception; and "Time to Pregnancy in Normal Fertility" (TTP) (2003–2006), a parallel-randomised trial, which aimed to assess the impact of CrM use on time to pregnancy in couples of proven fertility trying to conceive. Each of the cohorts aimed to include heterosexually active couples with normal fecundity. Eligibility criteria were assessed by women's responses to the CrM general intake form and/or a screening questionnaire. Eligibility requirements in the original studies included women, age 18–40 years old (upper limit of 35 years for TTP), not pregnant at entry, having regular menstrual bleeding, and not breast feeding (CMFS and TTP), or if breast feeding, not doing so exclusively (CEIBA). Recent users of oral contraceptives had to have at least one menstrual bleed (CEIBA) or two menstrual bleeds (TTP) since stopping the oral contraceptives; however, for CMFS there was no restriction for time since discontinuing oral contraceptives. All studies also required normal menstrual patterns since last use of depo-medroxy-progesterone acetate or a hormonal intra-uterine device.
