UBC Centre for Menstrual Cycle and Ovulation Research, Vancouver, BC, Canada.
BC Women's Health Research Institute, Vancouver, BC, Canada.
Hum Reprod. 2024 Nov 1;39(11):2565-2574. doi: 10.1093/humrep/deae215.
What is the relative length variance of the luteal phase compared to the follicular phase within healthy, non-smoking, normal-weight, proven normally ovulatory, premenopausal women with normal-length menstrual cycles?
Prospective 1-year data from 53 premenopausal women with two proven normal-length (21-36 days) and normally ovulatory (≥10 days luteal) menstrual cycles upon enrollment showed that, despite 29% of all cycles having incident ovulatory disturbances, within-woman follicular phase length variances were significantly greater than luteal phase length variances.
Many studies report menstrual cycle variability, yet few describe variability in follicular and luteal phase lengths. Luteal lengths are assumed 'fixed' at 13-14 days. Most studies have described follicular and luteal phase variability between-women.
STUDY DESIGN, SIZE, DURATION: This study was a prospective, 1-year, observational cohort study of relative follicular and luteal phase variability both between and within community-dwelling women with two documented normal-length (21-36 days) and normally ovulatory (≥10 days luteal phase) menstrual cycles prior to enrollment. Eighty-one women enrolled in the study and 66 women completed the 1-year study. This study analyzed data from 53 women with complete data for ≥8 cycles (mean 13).
PARTICIPANTS/MATERIALS, SETTING, METHODS: Participants were healthy, non-smoking, of normal BMI, ages 21-41 with two documented normal-length (21-36 days) and normally ovulatory (≥10 days luteal phase) menstrual cycles prior to enrollment. Participants recorded first morning temperature, exercise durations, and menstrual cycle/life experiences daily in the Menstrual Cycle Diary. We analyzed 694 cycles utilizing a twice-validated least-squares Quantitative Basal Temperature method to determine follicular and luteal phase lengths. Statistical analysis compared relative follicular and luteal phase variance in ovulatory cycles both between-women and within-woman. Normal-length cycles with short luteal phases or anovulation were considered to have subclinical ovulatory disturbances (SOD).
The 1-year overall 53-woman, 676 ovulatory cycle variances for menstrual cycle, follicular, and luteal phase lengths were 10.3, 11.2, and 4.3 days, respectively. Median variances within-woman for cycle, follicular, and luteal lengths were 3.1, 5.2, and 3.0 days, respectively. Menstrual cycles were largely of normal lengths (98%) with an important prevalence of SOD: 55% of women experienced >1 short luteal phase (<10 days) and 17% experienced at least one anovulatory cycle. Within-woman follicular phase length variances were greater than luteal phase length variances (P < 0.001). However, follicular (P = 0.008) and luteal phase length (P = 0.001) variances, without differences in cycle lengths, were greater in women experiencing any anovulatory cycles (n = 8) than in women with entirely normally ovulatory cycles (n = 6).
LIMITATIONS, REASONS FOR CAUTION: Limitations of this study include the relatively small cohort, that most women were White, initially had a normal BMI, and the original cohort required two normal-length and normally ovulatory menstrual cycles before enrollment. Thus, this cohort's data underestimated population menstrual cycle phase variances and the prevalence of SOD.
Our results reinforce previous findings that the follicular phase is more variable than the luteal phase in premenopausal women with normal-length and ovulatory menstrual cycles. However, our study adds to the growing body of evidence that the luteal phase is not predictably 13-14 days long.
STUDY FUNDING/COMPETING INTEREST(S): This medical education project of the University of British Columbia was funded by donations to the Centre for Menstrual Cycle and Ovulation Research. The authors do not have any conflicts of interest to disclose.
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在健康、不吸烟、体重正常、已证明正常排卵、绝经前、月经周期正常的女性中，与卵泡期相比，黄体期的相对长度变化是怎样的？
53 名绝经前女性的前瞻性 1 年数据显示，在入组时，所有周期中有 29%发生了排卵紊乱事件，但在同一个体中，卵泡期长度的变化明显大于黄体期长度的变化。这 53 名女性在入组前均有两次已知正常长度（21-36 天）和正常排卵（黄体期≥10 天）的月经周期。
许多研究报告了月经周期的可变性，但很少有研究描述卵泡期和黄体期长度的变化。黄体期长度被假定为 13-14 天。大多数研究都描述了在女性之间的卵泡期和黄体期的变化。
研究设计、规模、持续时间：本研究是一项前瞻性、1 年、观察性队列研究，研究了在入组前有两次已知正常长度（21-36 天）和正常排卵（黄体期≥10 天）的月经周期的社区居住女性的卵泡期和黄体期相对变化，包括个体内和个体间的变化。81 名女性入组了该研究，其中 66 名女性完成了 1 年的研究。本研究分析了 53 名女性的数据，这些女性至少有 8 个周期（平均 13 个）的数据完整。
参与者/材料、设置、方法：参与者为健康、不吸烟、体重正常、年龄在 21-41 岁之间，入组前有两次已知正常长度（21-36 天）和正常排卵（黄体期≥10 天）的月经周期。参与者每天在月经周期日记中记录第一晨温、运动时间和月经周期/生活经历。我们使用两次验证的最小二乘定量基础体温法分析了 694 个周期，以确定卵泡期和黄体期的长度。统计学分析比较了在排卵周期中，个体间和个体内的卵泡期和黄体期的相对变化。黄体期短或无排卵的正常周期被认为存在亚临床排卵障碍（SOD）。
在 1 年的研究中，53 名女性的 676 个排卵周期的平均长度分别为 10.3、11.2 和 4.3 天，卵泡期和黄体期的平均长度分别为 10.3、11.2 和 4.3 天。个体内的周期、卵泡期和黄体期的平均长度分别为 3.1、5.2 和 3.0 天。大多数月经周期的长度基本正常（98%），SOD 的患病率很高：55%的女性经历了黄体期<10 天的缩短，17%的女性经历了无排卵周期。个体内的卵泡期长度变化大于黄体期长度变化（P<0.001）。然而，在经历任何无排卵周期（n=8）的女性中，卵泡期（P=0.008）和黄体期长度（P=0.001）的变化，而周期长度没有差异，大于经历完全正常排卵周期的女性（n=6）。
局限性、谨慎的原因：本研究的局限性包括相对较小的队列、大多数女性是白人、最初的 BMI 正常，以及原始队列在入组前需要有两个正常长度和正常排卵的月经周期。因此，该队列的数据低估了人群月经周期阶段的变化和 SOD 的患病率。
我们的研究结果强化了之前的研究发现，在月经周期正常和排卵的绝经前女性中，卵泡期比黄体期的变化更大。然而，我们的研究增加了越来越多的证据，即黄体期的长度不一定是 13-14 天。
研究资金/利益冲突：不列颠哥伦比亚大学的这项医学教育项目由捐赠给月经周期和排卵研究中心的款项资助。作者没有任何利益冲突需要披露。
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