Study question Is there a relationship between day length and ovulation rate in women of reproductive age? Summary answer Analysis showed that increasing day length is associated with higher ovulation rate in women of reproductive age in both Sweden and the United States (US). What is known already Historically, winter months have been characterised by threatening survival conditions, such as reduced food availability and lower temperatures. Day length, or photoperiod, provides a reliable indication of upcoming seasonal changes, which promotes season-specific adaptations to behaviours and reproductive systems in mammals. To avoid the survival threats the winter months present, mammals with long gestation periods typically exhibit increased breeding as photoperiods increase. As humans also possess long gestation periods, it may be that humans similarly adapt to increasing photoperiods by exhibiting seasonal shifts in reproductive functioning. Study design, size, duration This retrospective analysis of basal body temperature (BBT) data from the Natural Cycles contraceptive app included approximately 115,000 Natural Cycles users’ data, amounting to approximately 1.3 million cycles from May 2014 - January 2021. BBT was used to confirm ovulation, the rate of which was calculated and compared to the number of hours daylight users experienced based on the geographical location in which they had registered for the app. Participants/materials, setting, methods We exclude cycles with missing data for any of the studied variables leaving ∼180k Swedish and ∼150K US cycles. The Meteostat library supplied the temperature on the start date of each user cycle. The Suntime library was used to determine the number of hours of daylight users were exposed to on the start date of each cycle, which used the geographic coordinates of the users’ reported country of residence. Main results and the role of chance Menstrual Cycle data from approximately 115 thousand Natural Cycles app users aged between 18-62 from two geographic groups, Sweden and the US. Data from cycles during and immediately following the event of a miscarriage, pregnancy, or instance of taking an emergency contraceptive, as well as the two cycles immediately following a completed pregnancy. Using a generalised logistic mixed-effects model, implementation via GPBoost, user-specific variation in ovulation rate as a function of location-specific day length was assessed while controlling for age, cycle length, body mass index (BMI), daily temperature, and education level. We find that day length is significantly correlated with higher ovulation (p < 0.01) in both the US and Swedish cohort. Limitations, reasons for caution Ovulation rate and day length may have emerged as a function a several underlying mechanisms, including the optimisation of conditions for childbirth, the optimisation of conditions for conception and early embryonic development, or a decrease in ovulation during the darker, winter months as a result of investment in immune function. Wider implications of the findings Photoperiod may be an important regulator of human reproductive activity, providing some preliminary evidence of seasonal changes to women’s ovulatory functioning. Furthermore, birth rate as a measurement of seasonal reproductive patterns in humans may not be as stable or accurate a measure for contemporary analyses of women’s reproductive functioning. Trial registration number 000000

中文翻译：

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P-631 日长预测女性生殖功能的排卵变化

研究问题 育龄妇女的日照长度和排卵率之间是否存在关系？摘要答案 分析表明，在瑞典和美国 (US)，日长增加与育龄妇女较高的排卵率有关。已知情况 从历史上看，冬季月份的特征是威胁生存条件，例如食物供应减少和温度降低。日长或光周期为即将到来的季节性变化提供了可靠的指示，这促进了哺乳动物对行为和生殖系统的特定季节适应。为了避免冬季月份的生存威胁，妊娠期长的哺乳动物通常会随着光周期的增加而增加繁殖。由于人类也有较长的妊娠期，可能是人类通过表现出生殖功能的季节性变化来适应增加的光周期。研究设计、规模、持续时间 这项对 Natural Cycles 避孕应用程序的基础体温 (BBT) 数据的回顾性分析包括约 115,000 名 Natural Cycles 用户的数据，从 2014 年 5 月至 2021 年 1 月总计约 130 万个周期。BBT 用于确认排卵率是根据用户注册该应用程序的地理位置计算得出的，并与用户在白天经历的小时数进行比较。参与者/材料、设置、方法 我们排除了任何研究变量的数据缺失的周期，留下约 180k 瑞典和 150K 美国周期。Meteostat 库提供每个用户周期开始日期的温度。Suntime 库用于确定用户在每个周期的开始日期暴露在日光下的小时数，它使用用户报告的居住国的地理坐标。主要结果和机会月经周期数据的作用来自瑞典和美国两个地理组的大约 115,000 个自然周期应用程序用户，年龄在 18-62 岁之间。流产、怀孕或服用紧急避孕药期间和之后的周期数据，以及完全怀孕后的两个周期数据。使用广义逻辑混合效应模型，通过 GPBoost 实施，在控制年龄、周期长度、体重指数 (BMI)、每天的温度和受教育程度。我们发现，在美国和瑞典队列中，日长与较高的排卵率（p < 0.01）显着相关。限制，谨慎的原因 排卵率和日长可能已经成为几个潜在机制的函数，包括优化分娩条件、优化受孕条件和早期胚胎发育，或在较暗的冬季排卵减少几个月作为免疫功能投资的结果。研究结果的更广泛影响光周期可能是人类生殖活动的重要调节因子，为女性排卵功能的季节性变化提供了一些初步证据。此外，出生率作为衡量人类季节性生殖模式的指标，可能不像当代女性生殖功能分析那样稳定或准确。试用注册号 000000