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Updated: Jun 8, 2026

Rodent Estrous Cycle Monitoring Utilizing Vaginal Lavage: No Such Thing As a Normal Cycle
Published on: August 30, 2021
Menstrual cycles are influenced by sunshine
Konstantin V Danilenko1, Oksana Y Sergeeva, Evgeniy G Verevkin
1Institute of Internal Medicine, Siberian Branch of the Russian Academy of Medical Sciences, Novosibirsk, Russia. kvdani@mail.ru
Introduction:
The study determined the effect of seasons and meteorological variables on ovarian-menstrual function.
Methods:
Women (N=129) living in Novosibirsk (55°N), Russia, provided data on normal menstrual cycles for over 1 year between 1999 and 2008. Of these, 18 together with 20 other healthy women were investigated once in winter and once in summer in 2006-2009. The investigated variables included serum levels of follicle-stimulating hormone (FSH), luteinising hormone (LH) and prolactin on day ∼ 7 of the menstrual cycle, ovary follicle size (by ultrasound) on day ∼ 12 and ovulation occurrence on subsequent days.
Results:
In summer vs. winter, there was a trend towards increased FSH secretion, significantly larger ovarian follicle size, higher frequency of ovulation (97% vs. 71%) and a shorter menstrual cycle (by 0.9 days). LH and prolactin levels did not change. In all seasons combined, increased sunshine (data derived from local meteorological records) 2-3 days before the presumed ovulation day (calculated from the mean menstrual cycle) led to a shorter cycle length. Air/perceived temperature, atmospheric pressure, moon phase/light were not significant predictors.
Conclusions:
Ovarian activity is greater in summer vs. winter in women living in a continental climate at temperate latitudes; sunshine is a factor that influences menstrual cycle.
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