The 89th Annual Meeting of the American Association of Physical Anthropologists (2020)

The circle game: is seasonal workload responsible for birth seasonality?


1Department of Environmental Health, Jagiellonian University Medical College, 2Department of Nursing Management and Epidemiological Nursing, Jagiellonian University Medical College

April 16, 2020 , Platinum Ballroom Add to calendar

Human birth seasonality is common in many populations. While social and climatological factors are usually suggested to be responsible for this phenomenon, energetic factors that influence female fecundity should be also considered. Physical activity causes decline in ovarian hormone levels, less frequent ovulations, and consequently, a lower probability of conception. In the past, farm work was highly seasonal and labour-intensive. In rural Poland, high energy expenditure during harvest and haying season (July-August) remained in contrast to fall and winter when women had lower involvement in agricultural work. Such variation has the potential to affect seasonal birth rate through suppressing ovarian function. Moreover, seasonal patterns in births may gradually change because of changes over time in an important exposure i.e. workload. However, despite of evidence that physical work supresses ovarian function, few previous studies have convincingly shown that seasonal workload may also influence birth rate.

We test the relationship between seasonal workload and seasonality of births using parish records from a village in Southern Poland. We examine whether monthly number of births changed over a 200-year period from 1783 to 2005. The whole period was divided into 20-year bins and seasonality in each time period was assessed.

We have not observed predicted differences in birth seasonality over time. The highest occurrence of conceptions was observed between March-June and lowest frequency of conceptions was observed between September-December. Our results did not confirm that seasonal workload affected probability of conception and we did not observe predicted changes in seasonality pattern over time.

This study was supported by Salus Publica Foundation and National Science Centre (grant no. 2016/21/D/NZ8/01306).