Seasonal Patterns in Human Reproductive Outcomes

Human reproduction exhibits marked temporal variation, with birth rates and conception outcomes fluctuating across the calendar year. These patterns arise from a complex interplay of environmental factors such as temperature and photoperiod, cultural rhythms including holidays and social customs, and individual sociodemographic characteristics. Seasonal influences may act indirectly through modulation of human physiology—altering gamete quality, hormone levels and implantation success—or directly via behaviour, such as timing of intercourse or deliberate family planning to coincide with favourable seasons. Assisted reproduction technologies, including in vitro fertilisation, provide additional insight by isolating environmental variables from social choices, revealing the extent to which ambient conditions impact clinical outcomes. The global significance of these rhythms spans obstetric preparedness, resource allocation and public health planning, while also informing mechanisms of human adaptation to changing climates and lifestyles.

Research from Nature Portfolio

Recent studies have synthesised global datasets to investigate how maternal birth season influences fertility later in life. A systematic meta-analysis across diverse human populations identified correlations between birth month and adult reproductive performance, suggesting that temperature and rainfall interplay may underlie the observed associations. In parallel, large‐scale clinical work on assisted conception has probed the effect of calendar season on in vitro fertilisation success, finding that when adjusting for patient age, treatment protocols and environmental covariates, live birth rates remain broadly consistent throughout the year. These foundational contributions clarify that while developmental exposures linked to birth season may subtly shape lifetime fertility, the controlled environment of assisted reproduction largely mitigates overt seasonal effects on immediate pregnancy outcomes.

Seasonal Patterns in Human Reproductive Outcomes publication trend

The graph below shows the total number of articles in seasonal patterns in human reproductive outcomes across all publications each year (not limited to Nature Index journals).

Technical terms

Fecundity: The biological capacity of an individual or couple to conceive, often expressed as the probability of conception per menstrual cycle.

Seasonality of births: The systematic variation in the number of births occurring in different seasons of the year.

In vitro fertilisation (IVF): An assisted reproductive technology in which oocytes are fertilised by sperm outside the body, with resulting embryos transferred to the uterus.

Meta-analysis: A statistical approach that combines results from multiple studies to derive a more precise estimate of effect size.

Embryo transfer: The procedure by which one or more embryos are placed into the uterine cavity during an IVF cycle.

References

1. Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms. Scientific Reports (2020).
2. Seasonal variability does not impact in vitro fertilization success. Scientific Reports (2019).
3. Changing seasonal variation in births by sociodemographic factors: a population-based register study. Human Reproduction Open (2018).
4. The effects of daily meteorological perturbation on pregnancy outcome: follow-up of a cohort of young women undergoing IVF treatment. Environmental Health (2019).
5. Seasonal fluctuation of in vitro fertilization encounters in the United States. Journal of Assisted Reproduction and Genetics (2023).