Do We Still Conceive With the Seasons? What Science Reveals About Light, Hormones, and Human Fertility

By Dr. Chelsea Dakers, ND; Assissted by AI

Every year, nature tugs at us in ways we don’t fully understand. We feel it in the pull toward quiet as autumn settles in, in the way light changes after the fall equinox, and—according to growing research—perhaps even in the body’s quiet readiness to create life.

Could it be that human fertility still dances with the seasons?

The answer appears to be yes… just more softly than before.

🌗 After the Equinox: A Subtle Call to Conceive

Many mammals experience seasonal fertility cycles. As the days shorten after the fall equinox, their bodies prepare to reproduce—so that births arrive in spring or summer, when survival odds are highest.

Humans aren’t all that different. In higher latitudes, birth records reveal a clear seasonal signal: more babies are born in late summer, suggesting that conceptions spike in the months following the autumn equinox (Lam & Miron, 1996).

It turns out that this timing aligns with increased melatonin secretion—a hormone released in response to darkness that influences our reproductive hormonal axis. Melatonin communicates with the hypothalamus, subtly modulating the release of GnRH, LH, and FSH—key hormones in ovulation and sperm production (Reiter et al., 2021).

In short: longer nights might quietly nudge our bodies toward reproduction.

A Tale of Two Climates: The Equator vs. the North

This pattern doesn’t show up everywhere. Near the equator, where daylight remains constant year-round, fertility patterns are more influenced by rainfall, agricultural cycles, and food security than by light.

In contrast, northern communities exhibit pronounced seasonality, with clear conception peaks after the autumn equinox and valleys during the bright, overstimulating months of late spring (Figa-Talamanca, 1980; Martinez-Bakker et al., 2014).

It’s as if our circadian system remembers a time when we, too, timed birth to warmer, safer months.

Why the Signal Is Fading in Modern Life

But here’s the fascinating part: that signal is fading.

With the widespread use of artificial lighting, climate control, and contraception, we’ve unhooked reproduction from its ancestral cues. Work schedules and fertility treatments have replaced the soft rhythm of light and dark.

Studies from Europe and North America show that while birth seasonality still exists, it’s less pronounced in urban populations and largely driven by cultural behaviors—such as holidays, school schedules, and social patterns (Doblhammer et al., 2013; Mouritsen et al., 2013).

Yet underneath, something ancient persists. Even in modern data, researchers found that biological fertility—not sexual activity—was the strongest driver of seasonal birth trends, especially in the Northern Hemisphere (Martinez-Bakker et al., 2020).

What This Means for Natural Fertility Work

As a clinician, I find this comforting. It reminds us that our bodies are not broken—they are responding to deeper rhythms, ones we can reconnect with.

For those trying to conceive naturally, this research opens a curious possibility: aligning fertility tracking and support protocols with seasonal rhythms may provide an added layer of wisdom. It also underscores the importance of restoring circadian balance, reducing nighttime light exposure, and creating space for melatonin to rise naturally.

You are not separate from the earth. Your hormonal wisdom is built from it.

References

Doblhammer, G., Choi, H., & Myrskylä, M. (2013). The weakening of the seasonal variation of births in developed countries. Demographic Research, 29, 155–186. https://doi.org/10.4054/DemRes.2013.29.6

Figa-Talamanca, I. (1980). Socioeconomic influences on birth seasonality in different geographic areas. Human Biology, 52(3), 421–438.

Lam, D. A., & Miron, J. A. (1996). The effects of temperature on human fertility. Demography, 33(3), 291–305. https://doi.org/10.2307/2061763

Martinez-Bakker, M., King, A. A., Rohani, P., & Bharti, N. (2020). Unraveling the seasonal cycles of fertility and birth. medRxiv. https://doi.org/10.1101/2020.11.19.20235010

Mouritsen, A., Larsen, E. C., Kristensen, S. G., & Andersen, C. Y. (2013). Seasonality of conception in Danish women. Human Reproduction, 28(11), 3185–3192. https://doi.org/10.1093/humrep/det326

Reiter, R. J., Sharma, R., & Ma, Q. (2021). Melatonin inhibits COVID-19-induced cytokine storm by reversing aerobic glycolysis in immune cells: A mechanistic analysis. Frontiers in Pharmacology, 12, 681582. https://doi.org/10.3389/fphar.2021.681582