Female Reproductive Performance and Maternal Birth Month: A Comprehensive Meta-Analysis Exploring Multiple Seasonal Mechanisms

Mary Regina Boland,Susanne Huber,Martin Fieder,Luis H John,Peter R Rijnbeek

doi:10.1038/s41598-019-57377-9

Mary Regina Boland, Susanne Huber + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-57377-9

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Abstract

Globally, maternal birth season affects fertility later in life. The purpose of this systematic literature review is to comprehensively investigate the birth season and female fertility relationship. Using PubMed, we identified a set of 282 relevant fertility/birth season papers published between 1972 and 2018. We screened all 282 studies and removed 131 non-mammalian species studies on fertility and 122 studies that were on non-human mammals. Our meta-analysis focused on the remaining 29 human studies, including twelve human datasets from around the world (USA, Europe, Asia). The main outcome was change in female fertility as observed by maternal birth month and whether this change was correlated with either temperature or rainfall. We found that temperature was either strongly correlated or anti-correlated in studies, indicating that another factor closely tied to temperature may be the culprit exposure. We found that rainfall only increases fertility in higher altitude locations (New Zealand, Romania, and Northern Vietnam). This suggests the possibility of a combined or multi-factorial mechanism underlying the female fertility – birth season relationship. We discuss other environmental and sociological factors on the birth season – female fertility relationship. Future research should focus on the role of birth season and female fertility adjusting for additional factors that modulate female fertility as discussed in this comprehensive review.

Highlights

Maternal birth season effects female fertility outcomes[8], including in both hunter/gather societies (e.g., Hiwi of Venezuela)[9] and industrialized societies[8,10]
We performed a meta-analysis on the relationship between temperature at birth and female fertility later in life based on birth month using datasets from 12 sites around the world
We found that temperature at birth was strongly negatively correlated with female fertility later in life only in certain regions

Summary

Introduction

Maternal birth season effects female fertility outcomes[8], including in both hunter/gather societies (e.g., Hiwi of Venezuela)[9] and industrialized societies[8,10]. The known relationship between temperature and fertility[6] could manifest itself in a birth season relationship. The main biological mechanism underlying a birth season relationship with female fertility remains the hypothesis that oocytes’ exposure to high temperatures at birth and shortly thereafter results in increased oocyte www.nature.com/scientificreports loss early in life[10,12,13,14]. Researchers posit that this initial reduction in oocyte volume at the time of the woman’s birth thereby reduces a woman’s fertility when she goes to bear children of her own later in life. This systematic review will comprehensively explore the literature underlying the maternal birth season – impaired female fertility paradigm while drawing from research conducted in humans. We will discuss hypotheses supported by the literature and corresponding biological mechanisms to understand the effects observed in the literature and to place these findings in broader scientific context

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