We will also 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. This systematic review will comprehensively explore the literature underlying the maternal birth season вЂ“ impaired female fertility paradigm while drawing from research conducted in humans. In addition, there are many studies among cows kept for dairy purposes, demonstrating the important role of temperature in female conception rates 19, 20, 21. Therefore, researchers posit that this initial reduction in oocyte volume at the time of the womanвЂ™s birth thereby reduces a womanвЂ™s fertility when she goes to bear children of her own later in life. Oocyte count is thought to be linked to fertility 18. Importantly, the female reproductive system, unlike males, is established early with females being born with their lifetime maximum number of oocytes 15, 16, 17. The main biological mechanism underlying a birth season relationship with female fertility remains the hypothesis that oocytesвЂ™ exposure to high temperatures at birth and shortly thereafter results in increased oocyte loss early in life 10, 12, 13, 14. In addition, the known relationship between temperature and fertility 6 could also manifest itself in a birth season relationship. Birth season can affect later risk of disease through alterations in the prenatal environment that alter growth patterns and processes 11. 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. Although at least one study points to other factors besides temperature that play a role more significant role at the country-level on female fertility 7.

Dairy researchers found that a cool, low-temperature, environment appeared to preserve fertility and reduce the risk of reproductive disorders 6 furthering support for a relationship between temperature and female fertility. In addition to rising infertility rates among humans, increases in infertility and reproductive disorders were observed in dairy cows 6. In developing countries, the rate of infertility is estimated at 1 in 4 couples 4, 5. European countries show similarly high infertility rates with Great Britain at 17% 3. Over 12% of reproductive age women (15вЂ“44 years) in the United States of America suffer from infertility or impaired fecundity 1, with some estimates as high as 16% 2. 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. We discuss other environmental and sociological factors on the birth season вЂ“ female fertility relationship. This suggests the possibility of a combined or multi-factorial mechanism underlying the female fertility вЂ“ birth season relationship. We found that rainfall only increases fertility in higher altitude locations (New Zealand, Romania, and Northern Vietnam). 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. 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.

Our meta-analysis focused on the remaining 29 human studies, including twelve human datasets from around the world (USA, Europe, Asia). We screened all 282 studies and removed 131 non-mammalian species studies on fertility and 122 studies that were on non-human mammals. Using PubMed, we identified a set of 282 relevant fertility/birth season papers published between 19. The purpose of this systematic literature review is to comprehensively investigate the birth season and female fertility relationship.

Globally, maternal birth season affects fertility later in life.

Comprehensive meta analysis for windows