Restored Sleep, Reduced Stress, and Mitigated Heat Stress on Sperm… Seasonal Changes Alter Fertility
“Pregnancy happens more easily after the rainy season ends.”
Among doctors who have long practiced in fertility clinics, this story has been passed down for years. In fact, some medical staff share their experiences, saying, “It seems that natural pregnancies or In Vitro Fertilization (IVF) pregnancies increase slightly when early autumn arrives.”
So, does pregnancy really increase after the rainy season ends?
Starting with the conclusion: the rainy season itself does not create pregnancy. However, it is highly likely that the seasonal shift that follows the rainy season creates a more favorable environment for reproductive function. Recent reproductive medicine is uncovering that pregnancy is not just a matter of eggs and sperm, but a complex physiological phenomenon influenced by sleep, stress, body temperature, sunlight, and lifestyle rhythms.
The changes that follow the end of the rainy season are more significant than one might think. When the days of rain stop and the sun begins to shine, people’s lifestyle patterns shift. Lingering humidity decreases, and outdoor activities increase. Many people get deeper sleep at night, and their moods feel lighter. While these might seem like simple mood changes, the biological clocks that regulate reproductive hormones within our bodies begin to move back onto a normal track.
The human body is more sensitive to seasonal changes than we realize. Sunlight regulates the secretion of melatonin and cortisol, and sleep stabilizes the hormonal rhythms of the hypothalamus and pituitary gland. This process has a non-negligible impact on ovulation in women and sperm production in men. Therefore, the changes after the rainy season should be viewed not as the direct cause of pregnancy, but as an environment that cultivates a physical state better suited for pregnancy.
Seasons are especially crucial for men.
Sperm are produced most healthily at a temperature about 2–4°C lower than the body temperature—which is why the testicles are located outside the body. Research consistently reports that if extreme summer heat and tropical nights continue, the increased testicular temperature can lower sperm motility and DNA stability.
In fact, there have been reports from Europe and North America that semen analysis results temporarily worsened in years with severe heatwaves. High-temperature environments can affect not only the count of sperm but also their fertilizing capacity.
The relatively cool period after the rainy season, before the peak heat of summer fully sets in, is a time when such heat stress is somewhat reduced. If accompanied by sufficient sleep and a regular lifestyle, the environment in which sperm are produced can become more stable.
Of course, sperm quality does not suddenly improve because it got cooler for a day or two. It takes about 70–80 days to produce a single sperm. However, if seasonal changes persist, there is a possibility that reproductive function will be influenced little by little.
Women are no exception.
Ovulation is regulated by a very delicate hormonal system. Chronic stress and sleep deprivation increase cortisol, a stress hormone, and can disrupt the normal rhythms of GnRH, LH, and FSH that regulate ovulation. The gloomy weather and stifling environment that persist during the rainy season often increase feelings of depression and fatigue. Conversely, when the rainy season ends, sunlight increases, and lifestyle rhythms stabilize, the likelihood of reproductive hormones remaining more stable increases.
This period is also meaningful for women preparing for IVF. Recently, fertility treatments emphasize the importance of sleep and stress management as much as medication. While embryo quality is determined in the lab, the entire body’s condition has a significant impact on the process of the uterus accepting the embryo.
Then, does IVF success rate actually differ by season?
There is no clear conclusion on this yet. Global studies have compared success rates in summer vs. winter, and spring vs. autumn, but the results were not consistent. Some studies showed slightly higher rates in spring and autumn, while others found no seasonal difference.
Recently, the interpretation that the lifestyle changes occurring in those seasons are a far more important variable than the seasons themselves is gaining weight. Sleeping well, reducing stress, exercising appropriately, men avoiding excessive heat exposure to the testicles, and women maintaining a regular routine have a much greater impact than the season itself.
In reality, lifestyle habits during the summer—such as keeping a laptop on your lap for long periods, driving for hours, or frequently using saunas and hot baths—can be detrimental to male reproductive function. Similarly, if women stay up late looking at smartphones and suffer from a lack of sleep, the likelihood of hormonal imbalance increases.
We cannot conclude that pregnancy suddenly increases just because the rainy season is over. However, the process of the body recovering and the lifestyle rhythm returning to normal after the rains can certainly be a positive signal for couples preparing for pregnancy.
Infertility treatment often looks like a competition of the latest medical technologies. However, reproductive medicine experts worldwide all say the same thing: as important as the technology to create a good embryo is the lifestyle habit to create a ‘good body.’ Pregnancy is not a piece of luck that arrives suddenly one day, but a process of life that begins at the moment the body is prepared.
※ This article was written based on domestic and international reproductive medicine and environmental health research, the latest research findings on heat stress in male sperm and female reproductive hormones, and expert opinions. It does not replace a specific individual’s diagnosis or treatment, and actual medical judgment must be made through consultation with a specialist.
※ Image: Created using generative AI (ChatGPT, OpenAI); depicts fictional individuals, not real people.