Nature works on a pretty tight schedule. We can even plan our vacations around it, knowing which week we’ll catch the best foliage or what day the cherry blossoms will bloom. The cycle of birth and death in nature is virtually the same every year. As humans, we are certainly not exempt from this cycle, and seasonal changes do in fact have an effect on our fertility and ability to conceive. Like animals, we have a mating season. Because seasons vary around the world, our seasonal fertility is based on our location. In the United States, most births occur in the summer and early autumn, particularly between July and September.

Some research suggests this high volume of birth in the summer months could be a result of climate conditions during conception. Temperature and sunlight may play a role in the healthiness of the sperm, which would certainly affect the rates of conception. The high levels of conception might also have something to do with longer menstrual cycles and hormonal changes in women. However, this research is not entirely proven, because it’s difficult to isolate something as natural as seasonal changes in an experiment.

More likely, there is a high volume of births in the summer months because people have the most sexual intercourse in the late fall and winter months. As the temperature starts cooling down, people are indoors more often, so sexual intercourse is more likely. People are vacationing less and relaxing more in the autumn. In fact, some studies even show that infidelity is less common in the winter because humans naturally “hunker down” with their loved ones to bear the burden of winter together.

So, if you are trying to conceive and you’re wondering which season might be best, there might not be a time when your body is more apt to conceive. However, there will probably be a time when you and your partner are more sexually active, so your chances of conceiving will be higher in those months. Conception and pregnancy can be unpredictable, so putting a timestamp on it is useless in many ways. Without worrying too much about the calendar, try to conceive when you and your partner feel that it’s appropriate. While humans might have a “mating season”, we are not bound to it like other animals, which is a beautiful thing. We can conceive whenever we’d like regardless of the season.

Source: Martin Bobak et al: The Seasonality of Live Birth is Strongly Influenced by Socio-Demographic Factors. Human Reproduction Volume 16 Issue 7 pp. 1512-1517 2011